Irrumatio is a form of oral sex where a man thrusts his penis into someone else’s mouth, in contrast to fellatio where the penis is being actively orally excited by a fellator. The difference lies mainly in which party takes the active part. By extension, irrumatio can also refer to the sexual technique of thrusting the penis between the thighs of a partner (intercrural sex), or between the abdomens of two men.”Latin erotic terminology actually distinguishes two acts. First, fellation, in which the man’s penis is orally excited by the fellator. Second, irrumation, in which the man (the irrumator) … engages in motions by moving his hips and body in a rhythm of his own choice”. A Latin synonym for “irrumator” is labda (Varr. ap. Non. 70,11; Aus. Epigr. 126).In the ancient Roman sexual vocabulary, irrumatio is strictly a form of oral rape (os impurum), in which a man forces his penis into someone else’s mouth, almost always that of another man.
alternative form of irrumation
Vigorous oral sex; the active penetration of a mouth with a penis