still sow, n. — Green’s Dictionary of Slang

still sow n.

[pvb ‘the still sow eats up half the draff’, i.e. the quiet pig eats more than its share of fodder]

1. a sly knave.

1611

Florio Queen Anna’s New World of Words n.p.: Acqua queta, [...] a close, slie, lurking knaue, a stil sow as we say.

2. a prostitute.

1709

N. Ward Secret Hist. of Clubs 171: Damn’d filing Whores, still Sows, and Fireships.