[ seks ]
/ sɛks /
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verb (used with object)
to ascertain the sex of or assign a sex to, especially newly-hatched chicks.
Verb Phrases
sex up, Informal.
  1. to arouse sexually: The only intent of that show was to sex up the audience.
  2. to increase the appeal of; to make more interesting, attractive, or exciting: I needed to sex up my résumé with bold fonts and snappy formatting.
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Idioms about sex

    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

See gender1.


1. sects, sex 2. gender, sex

Other definitions for sex (2 of 3)

[ seks ]
/ sɛks /

adjective Latin.

Other definitions for sex (3 of 3)


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

Origin of sex-

<Latin, combining form of sexsix
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use sex in a sentence

British Dictionary definitions for sex (1 of 2)

/ (sɛks) /

of or concerning sexual matterssex education; sex hygiene
based on or arising from the difference between the sexessex discrimination
(tr) to ascertain the sex of

Word Origin for sex

C14: from Latin sexus; compare secāre to divide

British Dictionary definitions for sex (2 of 2)


combining form

Word Origin for 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 ]

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.