sexual intercourse

   copulation

   Not just dealings or conversation between individuals. Now standard English:

    If he gets pinched with a girl in a hotel room, stop sexual intercourse. (Chandler, 1953)

   Sexual commerce is archaic, and there was no suggestion in the phrase that anybody was getting paid for their services.

   Sexual congress does not refer to goings-on on or around Capitol Hill:

    Eight days later in the little summer house, sexual congress took place. (Boyd, 1987)

   Sexual conjunction sounds more like differentiating grammatically between the masculine and feminine cases:

    ... a woman who could not be held back from strangers' rooms, who would have sexual conjunction whether in stinking rest rooms or mop cupboards. (Proulx, 1993)

   Sexual knowledge, which is usually had by an adult male with an under-age girl, does not mean simply that she has been told about the birds and the bees.

   Sexual relations may also imply familiarities short of copulation, and sexual relief refers to what the male obtains, implying that his health might suffer from an excess of celibacy.

   Sexual liaison in this sense is rare:

    [Mao] believed, as some Chinese emperors had believed, that sexual liaison with young virgins enhanced the chance of longevity in an old man. (Cheng, 1984 — or it made a convenient excuse)

   These concepts are further explored at commerce, congress, intercourse, know, etc.