Green’s Dictionary of Slang

callet n.

also callat, callot
[? Fr. cailette, a fool, lit. ‘a small quail’; Fr. calotte, a skullcap; Gaelic caille, a girl; Nares, Glossary (1822), suggests that ‘it is more likely to have been derived from the personage of [...] Callot, Kit. The fair, or perhaps more properly the brown associate of one Giles Hather. They are supposed to have been the first couple of English persons who took up the occupation of gipsies’]

[early 16C–18C] a whore, a promiscuous woman.