Green’s Dictionary of Slang

flirt n.

a prostitute.

1598		Florio Worlde of Wordes n.p.: Mucciaccia, a wench, a girle, a lasse, a harlot, a strumpet, a flurt, a minx, a trull, a gixie.
1600		N. Breton Pasquils Fooles-cap I 22: [She] that doth keepe an Inne for euery Guest [or] make a Smocke euen measure with a Shirt ... a Foolish flirt.
1611		R. Cotgrave Dict. of Fr. and Eng. Tongues n.p.: Gaultiere [...] A whore, punke, drab, queane, gill, flirt, strumpet, cockatrice, mad wench, common hackney, good one.
1676		Etherege Man of Mode II 1 72: An idle Town Flurt, with a painted Face.
1696		Motteux (trans.) Pantagruelian Prognostications (1927) II 693: Those whom Venus is said to rule as punks, jilts, flirts.

In compounds

flirt-gill (n.) (also flirt-gillian) [SE gill, a lass, a wench]

a prostitute; a promiscuous woman (cf. gill-flirt n.).

1595		Shakespeare Romeo and Juliet II iii: I am none of his flirt-gills; I am none of his skainsmates.
c.1607		Beaumont & Fletcher Knight of the Burning Pestle IV i: You heard him take me vp like a flirt Gill, and sing baudy songs vpon me.
1616		W. Haughton English-Men For My Money A3: And you, forsooth, you flur[t]gill, minion A brat scant folded in the dozens at most.
c.1617		Fletcher Chances III i: Thou took’st me up at every word I spoke As I had been a Mawkin, a flirt Gillian.
1713		Guardian 26: We are invested with a parcel of flirt-gills, who are not capable of being mothers of brave men [F&H].