Green’s Dictionary of Slang

1. a prostitute.

1865		Leaves from Diary of Celebrated Burglar 42/2: She kept a second rate ‘dossing crib,’ and one of the ‘moths’ who lived at her house, ‘picked up’ Charley one night.
1868		H.L. Williams Black-Eyed Beauty 22: Trying to come the ‘Ledger’ sort of virtue, eh, you crazy moth!
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 198: moth, a prostitute.
1935		A.J. Pollock Und. Speaks n.p.: Moth, a female of easy virtue.

2. (Irish) a woman, a girl-friend [common Irish English confusion of spoken t and th].

1995		A. Higgins Donkey’s Years 96: Rita is his moth.
1997		Share Slanguage.
2002		Blue Pages (Dublin) ‘Dublin Dictionary’ 🌐 A 3m A young male whose only cares are his ma, his moth and his moustache.