WordNet (r) 3.0 (2006):

sexual relation
    n 1: the act of sexual procreation between a man and a woman;
         the man's penis is inserted into the woman's vagina and
         excited until orgasm and ejaculation occur [syn: sexual
         intercourse, intercourse, sex act, copulation,
         coitus, coition, sexual congress, congress, sexual
         relation, relation, carnal knowledge]