noun

• (countable) A category into which sexually-reproducing organisms are divided on the basis of their reproductive roles in their species; the system of such categories, which can differ by organism or by taxonomic branch.
  "The effect of the medication is dependent upon age, sex, and other factors."
• (countable) Another category, especially of humans and especially based on sexuality or gender roles.
  "Still there are some loop-holes out of which a man may creep, and dare to think and act for himself; but for a woman it is an herculean task, because she has difficulties peculiar to her sex to overcome, which require almost super-human powers."
• (countable) The members of such a category, taken collectively.
  "the fairer sex"
• (uncountable) The distinction and relation between these categories, especially in humans; gender.
  "A lot of women now like men to pay for them on dates... We've dealt with the outdated view of sex underpinning this."

verb

• (zoology, transitive) To determine the sex of (an animal).
  "If we sex the cattle, which is the only way to get at their value, we shall have... 400 cows, 200 yearling heifers."
• (chiefly US, colloquial, transitive) To have sex with.
  "As good as Muddah had handled me in bed, sexing her hadn't done a damn thing to take my mind off my cousin Smoove."
• (chiefly US, colloquial, intransitive) To have sex.
  "Our baby is eighteen months old now, and cries when we sex"

noun

• (obsolete) Alternative form of sect.