sex_act has definitions from the fields of biology,sexuality
[ noun ] (biology,sexuality) 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

Used in print

(David Stacton, The Judges of the Secret Court....)

He did not really want to kill , but as in the sexual_act , there was a moment when the impulse took_over and could not be downed , even while you watched yourself giving_way to it .