Definitions of sex:

• noun:   the properties that distinguish organisms on the basis of their reproductive roles

  Example: "She didn't want to know the sex of the foetus"

• noun:   all of the feelings resulting from the urge to gratify sexual impulses

  Example: "He wanted a better sex life"

• noun:   either of the two categories (male or female) into which most organisms are divided

  Example: "The war between the sexes"

• noun:   activities associated with sexual intercourse

  Example: "They had sex in the back seat"

• verb:   tell the sex (of young chickens)
• verb:   stimulate sexually