Sex  —n. 1 each of the main groups (male and female) into which living things are categorized on the basis of their reproductive functions (what sex is your dog?). 2 sexual instincts, desires, etc., or their manifestation. 3 colloq. Sexual intercourse. 4 (attrib.) Of or relating to sex or sexual differences. —v. 1 determine the sex of. 2 (as sexed adj.) Having a specified sexual appetite (highly sexed). [latin sexus]