Green’s Dictionary of Slang

1. (UK Und.) an old woman [presumably a cantankerous one who ‘goes off with a bang’. In Henry IV Pt 1 Shakespeare uses the term in such a manner to describe the irascible ‘gunpowder Percy’].

c.1698		B.E. Dict. Canting Crew n.p.: Gun-powder an old Woman.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
1859		Matsell Vocabulum 39: gunpowder A scolding or quick-tempered woman.

2. (later use is US black) a fiery drink; prob. gin [the short-lived 18C UK use was revived in US black use].

1756		W. Toldervy Hist. of the Two Orphans III 112: Taking a dirty paper out of her bosom, in which was written the following words: Tape, glim, rushlight, white port, rasher of bacon, gunpowder, slug, wild-fire, knock-me-down, and strip-me-naked. [Ibid.] 118: Come, here’s t’ye, in a glass of gunpowder, d--n ye.
1983		Reader’s Digest Success with Words 85/2: Black English...gunpowder = ‘gin’.

3. (US drugs) opium.

1975

Hardy & Cull Drug Lang. and Lore.

4. (US drugs) cocaine.

1990

S. Morgan Homeboy 69: Front me a dime of your gunpowder, Firecracker.