The Collaborative International Dictionary of English v.0.48:

Coition \Co*i"tion\, n. [L. coitio, fr. coire to come together;
   co- + ire to go.]
   A coming together; sexual intercourse; copulation. --Grew.
   [1913 Webster]

WordNet (r) 3.0 (2006):

coition
    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]