I think that the clinical terms were "coitus" and "sexual intercourse" (the latter is more recent), though they would have only referred to the PiV variety. (I'm guessing that it was the development of the second term which led to "sex"'s modern meaning.) Other than these formal terms, yeah, it was largely euphemism-city-- either that or "vulgar" words which were not to be used in so-called "polite company". But my impression is that you just didn't speak of the subject at all in everyday discourse. At least directly; you would talk around it. And even then, the talk would mostly be about reproduction within marriage. Non-reproductive (and particularly same-sex) sexuality went mostly unacknowledged. In fact, until comparatively recently, I think there was little awareness that homosexuality or bisexuality even existed.