[ seks ]
See synonyms for sex on
  1. the male, female, or sometimes intersex division of a species, especially as differentiated with reference to the reproductive functions or physical characteristics such as genitals, XX and XY chromosomes, etc.

  2. a label assigned to a person at birth, usually male or female and sometimes intersex, and typically based on genital configuration.: See Usage note at the current entry.

  1. the sum of the structural and functional differences by which male, female, and sometimes intersex organisms are distinguished, or the phenomena or behavior dependent on these differences: These plants change sex depending on how much light they receive.

  2. sexual relations or activity, especially sexual intercourse: We hold a large collection of oral histories that explore changing attitudes to sex and marriage.

  3. the sexual instinct or attraction drawing one organism toward another, or its manifestation in life and conduct: Some disapprove of choosing a life partner based on sex.

  4. the genitals; genitalia: A towel was hiding his sex from view.

verb (used with object)
  1. to ascertain the sex of or assign a sex to, especially newly-hatched chicks.

Verb Phrases
  1. sex up, Informal.

    • to arouse sexually: The only intent of that show was to sex up the audience.

    • to increase the appeal of; to make more interesting, attractive, or exciting: I needed to sex up my resume with bold fonts and snappy formatting.

Idioms about sex

  1. to have sex, to engage in sexual relations, especially sexual intercourse.

Origin of sex

First recorded in 1350–1400; Middle English, from Latin sexus, perhaps akin to secāre “to divide” (see section)

usage note For sex

Human sex is often seen as strictly binary and composed only of male and female. It is certainly true that, when it comes to reproduction, there are two different cell types that combine to form an embryo: the sperm and the egg. People who think of sex as binary often assume that sex simply reflects whether a person produces eggs or sperm.
In practice, however, the way that a person's sex is categorized depends on several characteristics: genitals, chromosomes, hormonal profiles, and external physical features such as the development of extensive facial hair or breast tissue. These characteristics do frequently occur together. For example, the majority of people born with XX chromosomes are also born with ovaries that produce eggs, and most also go on to develop more breast tissue during puberty. Male and female, when used of sex, usually refer to people who fit more or less into these common patterns of co-occurring characteristics.
However, there are people born with physical characteristics that do not fit neatly into these categories. For example, some people have XY chromosomes, but their cells cannot respond to androgens, meaning that they may develop a vagina and more breast tissue. Others are born with gonads that do not produce either sperm or egg cells. There are also people born with chromosomes that are XXY. Such conditions may be called intersex conditions, disorders of sex development, or differences of sex development. These terms are broad labels that do not constitute a discrete third sex, but rather identify variation in physical characteristics that does not fit into the male-female binary.
Like anyone else, a person with any of these conditions may identify as a man, a woman, or any other gender. Furthermore, a person's sex characteristics may or may not influence their gender, or their relationship with their gender. See gender1, intersex.

Words that may be confused with sex

Other definitions for sex (2 of 3)

[ seks ]

  1. six.

Other definitions for sex- (3 of 3)


  1. a combining form, occurring in loanwords from Latin, meaning “six” (sexagenary); on this model used in the formation of compound words: sexpartite.

Origin of sex-

<Latin, combining form of sexsix Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

How to use sex in a sentence

  • Are you quite sure you have never suffered from this rather common disorder, gentle reader, at least, if you be of the male sex?

  • But if you restrict it, to the sense in which it is commonly applied to the angelic sex, I am not prepared to answer.

  • As public accuser, he caused the death of immense numbers, of all ages and either sex.

  • That he might lose his head and 'introduce an element of sex' was conscience confessing that it had been already introduced.

    The Wave | Algernon Blackwood
  • He respected her courage and obvious power to rise above the personal attitude of her sex.

    Ancestors | Gertrude Atherton

British Dictionary definitions for sex (1 of 2)


/ (sɛks) /

  1. the sum of the characteristics that distinguish organisms on the basis of their reproductive function

  2. either of the two categories, male or female, into which organisms are placed on this basis

  1. feelings or behaviour resulting from the urge to gratify the sexual instinct

  2. sexual matters in general

  1. of or concerning sexual matters: sex education; sex hygiene

  2. based on or arising from the difference between the sexes: sex discrimination

  1. (tr) to ascertain the sex of

Origin of sex

C14: from Latin sexus; compare secāre to divide

British Dictionary definitions for sex- (2 of 2)


combining form
  1. six: sexcentennial

Origin of sex-

from Latin

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 sex


[ sĕks ]

  1. Either of two divisions, male and female, into which most sexually reproducing organisms are grouped. Sex is usually determined by anatomy, the makeup of the sex chromosomes, and the type and amount of hormones produced. When the sex of an organism is determined by the sex chromosomes, males and females are generally produced in equal numbers. In other organisms, such as bees and wasps, in which females develop from fertilized eggs and males develop from unfertilized eggs, distribution of the sexes is unequal.

a closer look

Thanks to high school biology, we are accustomed to thinking of the sex of an organism as being determined by the chromosomes, notably the sex chromosome in humans (designated X or Y). But this is not the whole story, and it applies universally only to mammals and birds. In other animals sex is often determined by environmental factors and can be a variable phenomenon. In a species of slipper limpet (Crepidula fornicata), a kind of mollusk, all individuals begin life as females. Clinging to rocks and to each other, they form piles. The limpet on top of the pile changes into a male. If another limpet attaches itself on top of the male limpet, the newcomer becomes male, and the male limpet beneath it reverts to being female. These slipper limpets show the evolutionarily advanced feature of internal fertilization, and the male on top extends his reproductive organ down the pile of females below him to fertilize their eggs. For some fish, the number of males in the population determines the sex of the fish. If there are not enough males, some females become males. In these examples, the same animal can make fertile eggs and fertile sperm at different times in its life. These animals are not hermaphrodites, like some worms, but literally change sex. Some animals have only one sex. For instance, some species of lizards reproduce only by parthenogenesis-that is, their unfertilized eggs grow into adults, and these species no longer have males. Sometimes the external temperature determines the sex of an animal during its early development. If the eggs of the American alligator (Alligator mississippiensis) are incubated at above 34 degrees Celsius (93° F), all of the offspring become males. If they are incubated below 30 degrees Celsius (86° F), they become females. The midrange of temperatures results in both male and female offspring.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Other Idioms and Phrases with sex


see fair sex.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.