[ kan-ser ]
/ ˈkæn sər /
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See synonyms for: cancer / cancerous on Thesaurus.com

  1. a malignant and invasive growth or tumor, especially one originating in epithelium, tending to recur after excision and to metastasize to other sites.
  2. any disease characterized by such growths.
any evil condition or thing that spreads destructively; blight.
genitive Can·cri [kang-kree]. /ˈkæŋ kri/. (initial capital letter)Astronomy. the Crab, a zodiacal constellation between Gemini and Leo.
Cancer, Astrology.
  1. the fourth sign of the zodiac: the cardinal water sign.
  2. a person born under this sign, usually between June 21 and July 22.
tropic of Cancer. See under tropic (def. 1a).
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Origin of cancer

First recorded in 1350–1400; Middle English, from Latin: literally, “crab”; Latin stem cancr-, dissimilated from unattested carcr-, akin to Greek karkínos, Sanskrit karkata “crab”; see canker


Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does Cancer mean?

Cancer is the name of a constellation that’s interpreted as resembling a crab. It’s sometimes referred to as The Crab.

A constellation is a group of stars that appear near each other in the sky—especially a group that has been given a name. Cancer is considered one of the 12 zodiacal constellations—constellations that appear within a particular portion of the sky called the zodiac.

In astronomy, the zodiac is the band of sky along which the paths of the sun, the moon, and the planets appear to move.

Despite its basis in astronomy, the word zodiac is mainly associated with and most often used in the context of astrology, the nonscientific practice in which the positions of heavenly bodies at certain times are thought to influence or be correlated with human behavior and events. In astrology, zodiac refers to a diagram (often a circular one) representing the zodiac belt and showing the symbols associated with each of the 12 constellations or sections, which are called the signs of the zodiac. Cancer is one of these signs. It is situated between Gemini and Leo and is considered the fourth sign of the zodiac.

The other signs of the zodiac are Aries, Taurus, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.

The position of the sun in a particular portion of the zodiac at the moment of a person’s birth is thought to correlate with their personality. This is what people are referring to when they talk about their zodiac sign (or star sign or often just sign). People whose sign is Cancer are those born between June 21 and July 22.

In the context of the zodiac, the word Cancer can also be used as a noun to refer to someone who is born during this time, as in I was born in early July, so I’m a Cancer. The word Cancerian can be used to mean the same thing. It can also be used as an adjective form of Cancer.

Example: I’m a Cancer, but I don’t think I fit into the sensitive Cancer stereotype.

Cancer dates

People with the sign Cancer are traditionally considered to be those born in the range of June 21–July 22. However, interpretations vary.

Where does the word Cancer come from?

The first records of the word cancer in English come from the late 1300s. The word comes from Latin, in which it means “crab.” (The word cancer in reference to the disease comes from the same root, which can also be interpreted as meaning “creeping tumor.” The word canker referring to a sore comes from the same root.)

In ancient mythology, the constellation Cancer was associated with the crab that the goddess Hera sent to hinder Heracles (Hercules).

In astrology, the different signs of the zodiac are thought to be associated with certain personality traits. Traits associated with Cancer include loyalty and sensitivity. Cancer and the other signs of the zodiac are often used in the context of a person’s horoscope. The word horoscope can refer to a diagram of the heavens that maps the relative position of planets and the signs of the zodiac. It can also refer to a prediction based (or said to be based) on a person’s sign and the location of other celestial bodies at the time they were born.

The imaginary line that circles the globe about one-quarter of the way between the equator and the North Pole is called the Tropic of Cancer. It’s the point at which the Sun is directly overhead during the June solstice. (The line known as the Tropic of Capricorn is between the equator and the South Pole.)

It’s called the Tropic of Cancer because, when it was named, the Sun was in the constellation Cancer at the time of the June solstice.

Get more insight into what really defines a Cancer by visiting our article on the many traits of Cancers. 

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What are some other forms related to Cancer?

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What are some words that share a root or word element with Cancer

What are some words that often get used in discussing Cancer?

How is Cancer used in astronomy and astrology?

The word Cancer is used to refer to the constellation or the sign of the zodiac named after the constellation. In the context of astrology, people associate a number of different traits with the sign Cancer.

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True or False?

The constellation Cancer is situated between Gemini and Leo.

How to use cancer in a sentence

British Dictionary definitions for cancer (1 of 2)

/ (ˈkænsə) /

any type of malignant growth or tumour, caused by abnormal and uncontrolled cell division: it may spread through the lymphatic system or blood stream to other parts of the body
the condition resulting from this
an evil influence that spreads dangerously

Other words from cancer

Related prefix: carcino-

Derived forms of cancer

cancerous, adjectivecancerously, adverb

Word Origin for cancer

C14: from Latin: crab, a creeping tumour; related to Greek karkinos crab, Sanskrit karkata

British Dictionary definitions for cancer (2 of 2)

/ (ˈkænsə) /

noun Latin genitive Cancri (ˈkæŋkriː)
astronomy a small faint zodiacal constellation in the N hemisphere, lying between Gemini and Leo on the ecliptic and containing the star cluster Praesepe
  1. Also called: the Crab the fourth sign of the zodiac, symbol ♋, having a cardinal water classification and ruled by the moon. The sun is in this sign between about June 21 and July 22
  2. Also called: Moonchild a person born during a period when the sun is in this sign
tropic of Cancer See tropic (def. 1)
astrology born under or characteristic of Cancer
Also (for senses 2b, 4): Cancerian (kænˈsɪərɪən)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for cancer (1 of 2)

[ kănsər ]

A disease characterized by any of various malignant neoplasms composed of abnormal cells that tend to proliferate rapidly and invade surrounding tissue. Without treatment such as chemotherapy or radiation, cancer cells can metastasize to other body sites and cause organ failure and death.
A malignant tumor.

A Closer Look

The human immune system often fights off stray cancer cells just as it does bacteria and viruses. However, when cancer cells establish themselves in the body with their own blood supply and begin replicating out of control, cancer becomes a threatening neoplasm, or tumor. It takes a minimum of one billion cancer cells for a neoplasm to be detectable by conventional radiology and physical examinations. Cancer, which represents more than 100 separate diseases, destroys tissues and organs through invasive growth in a particular part of the body and by metastasizing to distant tissues and organs through the bloodstream or lymph system. Heredity, lifestyle habits (such as smoking), and a person's exposure to certain viruses, toxic chemicals, and excessive radiation can trigger genetic changes that affect cell growth. The altered genes, or oncogenes, direct cells to multiply abnormally, thereby taking on the aggressive and destructive characteristics of cancer. Treatments such as surgery, chemotherapy, and radiation are effective with many cancers, but they also end up killing healthy cells. Gene therapy attempts to correct the faulty DNA that causes the uncontrolled growth of cancer cells. Researchers are investigating other treatments, such as immunotherapy (the stimulation of the body's natural defenses), vectorization (aiming chemicals specifically at cancer cells), and nanotechnology (targeting cancer cells with minute objects the size of atoms).

Scientific definitions for cancer (2 of 2)


A faint constellation in the Northern Hemisphere near Leo and Gemini. Cancer (the Crab) is the fourth sign of the zodiac.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for cancer


A disease characterized by rapid growth of cells in the body, often in the form of a tumor. Cancer is invasive — that is, it can spread to surrounding tissues. Although this disease is a leading cause of death in the United States, research has provided considerable insight into its many causes (which may include diet, viruses, or environmental factors) and options for treatment (which include radiation, chemotherapy, surgery, and possibly gene therapy).

notes for cancer

The term cancer is often used to describe a nonmedical condition that is undesirable, destructive, and invasive: “Watergate was a cancer on the presidency.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.