Green’s Dictionary of Slang

to have sexual intercourse; also as n., sexual intercourse; thus smocking n.

c.1572		Valenger ‘Cockolds Kallender’ Arundel MS I 217: Fyne Hollond is not fitt for Coltes then seeke some better Smocking.
1623		Fletcher & Rowley Maid in the Mill IV i: You are going a smocking perhaps.
1675		T. Shadwell Delights of the Bottle in Ebsworth Roxburghe Ballads IV 45: Once in a Moneth [he] takes a touch of the Smock, And poor Nature upholds, with a bit and a knock.
1700		‘The Country-man’s Delight’ in Playford Pills to Purge Melancholy II 126: The Night is Spent / With more content, / For then we all agree, / To Cock it and Dock it, / Smock it and Knock it, / Under the Green-wood Tree.
1719		in D’Urfey Pills to Purge Melancholy IV 126: To Cock it and Dock, Smock and Knock it, Under the Green-wood Tree.
1738		Swift Polite Conversation 78: What? You don’t smoak, I warrant you, but you smock. (Ladies, I beg your Pardon.).