Irrumation

Irrumatio is the intercrural sex act of thrusting of the penis into the mouth of a partner, between the thighs, or between the abdomens of two men. In the ancient Roman sexual vocabulary, irrumatio is strictly a form of os impurum, oral rape, in which a man forces his penis into someone else's mouth, almost always that of another man.

"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).

The English noun irrumatio or irrumation and verb irrumate come from the Latin irrumare, to force one to perform fellatio. J. L. Butrica, in his review of R. W. Hooper's edition of The Priapus Poems, a corpus of poems known as Priapeia in Latin, states that "some Roman sexual practices, like irrumatio, lack simple English equivalents". There is some conjecture among linguists, as yet unresolved, that this noun may be derived from and an abbreviation of irruminatio and irruminare (Latin, rumen, ruminis, the mouth, throat and gullet, whence 'ruminate', to chew), therefore meaning 'the insertion into, to insert into the mouth or throat'.

As the quotation from Butrica suggests and an article by W. A. Krenkel shows, irrumatio was a distinct sexual practice in ancient Rome. J. N. Adams states that "it was a standard joke to speak of irrumatio as a means of silencing someone".Oral sex was considered to be an act of defilement: the mouth had a particularly defined role as the organ of oratory, as in Greece, to participate in the central public sphere, where discursive powers were of great importance. Thus, to penetrate the mouth could be taken to be a sign of massive power differential within a relationship. Erotic art from Pompeii depicts irrumatio along with fututio, fellatio and cunnilingus, and pedicatio or anal sex. The extant wall paintings depicting explicit sex often appear to be in bathhouses and brothels, and oral sex was something usually practiced with prostitutes because of their lowly status.

...
Wikipedia