Green’s Dictionary of Slang

the vagina; thus fig. for sexual intercourse (see cite 1779).

1584		Greene Mamillia II 187: [Clarynda was] wallowing in the waues of wantonnesse, and offering her incense at the altar of Venus.
1680		Behn Disappointment VI 179: His daring Hand that Altar seiz’d, Where Gods of Love do sacrifice: That Awful Throne, that Paradice Where Rage is calm’d.
1709		N. Chorier (trans.) of Meursius ‘The Delights of Venus’ in Cabinet of Love n.p.: On Venus Mount the hair a cov’ring made, / To hide love’s altar with an envious shade.
1727		E. Curll Batchelor-Keeper n.p.: About five the libidinous Pair returned from Love’s Altars; but in such a Dishabillee, as made it no Difficulty to imagine what sort of Devotions they had been paying.
1744		Machine 3: O venus! [...] cundum which to thy Altar nightly brings / Ten Thousand vig’rous unpolluted Things.
1749		Hist. of the Human Heart 127: From viewing their Faces, he bashfully cast his Eyes on the Altar of Love [...] The Throne of Love was thickly covered with jet-black Hair.
1758		New Atalantis 47: Alternate kissing of the two collateral columns [...] which lead to the blissful altar, veiled from vulgar eyes with the fringe of Venus.
1775		‘Miss Peggy Murray’ Ranger’s Impartial List of the Ladies of Pleasure in Edinburgh n.p.: She is also very coy, full of vivacity; and when she approaches the altar of love, she does it with all the modesty and sanctity of a vestal virgin.
1779		Nocturnal Revels I 13: Peg Woffington [...] often sacrificed at the altar of Venus in this chapel.
1821		‘An Amateur’ Real Life in London II 82: Having a desire to sink the shank, he enlisted under the banners of Cupid, paid his addresses to one of the Queen’s maids, carried the fortress by a coup de main, and gained a safe lodgement in the covert way, by taking the oath of allegiance at the altar of Hymen.
1889		C. Deveureux Venus in India I 30: Doubtless my steady married life with its regular hours, regular meals, and regular, never excessive sacrifices on the alter of venus had much to do with the steady power I felt so strong in me.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 20: Autel, m. 1. the female pudendum; ‘the altar of love’.