sex

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Sexual activity, especially sexual intercourse.
• noun The sexual urge or instinct as it manifests itself in behavior.
• noun Either of the two divisions, designated female and male, by which most organisms are classified on the basis of their reproductive organs and functions.
• noun The fact or condition of existing in these two divisions, especially the collection of characteristics that distinguish female and male.
• noun Females or males considered as a group.
• noun One's identity as either female or male.
• noun The genitals.
• transitive verb To determine the sex of (an organism).
• transitive verb To arouse sexually. Often used with up.
• transitive verb To increase the appeal or attractiveness of. Often used with up.

from The Century Dictionary.

• noun The character of being either male or female; the anatomical and physiological distinction between male and female, evidenced by the physical character of their generative organs, and the part taken by each in the function of reproduction; gender, with reference to living organisms.
• noun Either one of the two kinds of beings, male and female, which are distinguished by sex; males or females, collectively considered and contrasted.
• noun Especially, the female sex; womankind, by way of emphasis: generally with the definite article.
• noun In botany, the character or structure of plants which corresponds to sex in animals, there being, except in the lowest orders, a clear differentiation of male and female elements.
• noun the female sex collectively; womankind.
• To ascertain the sex of (a specimen of natural history); mark or label as male or female.
• noun An obsolete or dialectal form of six.

from the GNU version of the Collaborative International Dictionary of English.

• noun The distinguishing peculiarity of male or female in both animals and plants; the physical difference between male and female; the assemblage of properties or qualities by which male is distinguished from female.
• noun One of the two divisions of organic beings formed on the distinction of male and female.
• noun The capability in plants of fertilizing or of being fertilized.
• noun One of the groups founded on this distinction.
• noun the female sex; women, in general.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable Either of two main divisions (either female or male) into which many organisms can be placed, according to reproductive function or organs.
• noun uncountable The distinguishing property, quality, or assemblage of properties by which organisms are classified as female or male on the basis of their reproductive organs and functions; the set of properties by which male is distinguished from female.
• noun uncountable Sexual intercourse; the act of sexual intercourse.
• noun euphemistic Genitalia; a penis or vagina.
• noun obsolete Women; womankind.
• verb zoology To determine the biological sex of an animal.
• verb colloquial To have sex with.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun either of the two categories (male or female) into which most organisms are divided
• noun the properties that distinguish organisms on the basis of their reproductive roles
• noun activities associated with sexual intercourse
• verb stimulate sexually
• verb tell the sex (of young chickens)
• noun all of the feelings resulting from the urge to gratify sexual impulses