Green’s Dictionary of Slang

1. (also night-in-girl) a prostitute.

1632		D. Lupton London and the Countrey Carbonadoed 45: The Counters, they teach wandrings Nightingals the way vunto their Nests.
1824		Pierce Egan’s Life in London 26 Sept. 5/1: Those naughty night-in-girls over the water.
1984		Partridge DSUE (8th edn) 792/2: from ca. 1840.

2. (US) a singer.

1891		C. Townsend Negro Minstrels 37: Mose am a reg’lar nightingale.
1902		Ade Girl Proposition 169: She had herself Billed as a Nightingale. Often she went to Soirées and Club Entertainments, volunteering her Services.

3. (UK Und.) an informer [they SE sing/sing v. (5); note 18C milit. nightingale, a soldier who cries out during a flogging].

[c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Nightingale, a Soldier who cries out at the Halberds].
1938		D. Runyon ‘Cemetery Bait’ in Runyon on Broadway (1954) 524: There are many nightingales in these parts [...] and they will sing to the law on very slight provocation.
1961		J. Sparks Burglar to the Nobility 138: There’s a little bird called a Nick Nightingale that sings outside my bedroom window.
1968		‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 51: nightingale – A fink dropping a dime and singing his song.
1989		H. Rawson Dict. of Invective (1991) 71: In the underworld, a canary is another kind of ‘singer,’ i.e., an informer, a.k.a. nightingale, pigeon or rat.
1992		Bentley & Corbett Prison Sl. 35: Nightingale A police informant and or a prison snitch.

4. a £10-note, the reverse bears a picture of Flornce Nightingale.

2024

J. Meades Empty Wigs (t/s) 336: I salute the cleaners [...] I feel a cur if I don’t slip them a Nelson or a Nightingale.