sex is on the Basic English 850 List.
servant - sex - shade
sex is one of the 1000 most common headwords.
seven - sex - shall
sex is on the Academic Word List.

Pronunciation

change

Singular
sex

Plural
sexes

 
Two people having sex
  1. (uncountable) Sex is an act done by a male and a female (in this case there is sometimes an intent to make babies) or with just two men or women.
    Most men in our survey say they definitely would not have sex with a new partner without using a condom.
  2. (countable) A person or animal's sex is male, female, or both.
    She had not had any male friends during her early life and now found it difficult to talk to members of the opposite sex.