Green’s Dictionary of Slang

nailer n.

[lit. and fig. uses of nail v.]

1. a clincher, a ‘knockout’.

[UK]‘Bill Truck’ Man o’ War’s Man (1843) 262: Hang me, Joe, but that’s a complete nailer to ye, me lad.

2. a policeman.

[UK]‘Margate Steam Packet’ in Universal Songster I 14/1: Oyster dealers - fish-fags - sailors / Gentry - tradesmen - porters - nailers.
[UK]Era (London) 15 Aug. 3/3: The nailers [...] they are up to everything.
[UK]T. Taylor Ticket-Of-Leave Man Act I: dalton: The Crushers are getting to know too much; then there’s the nailer’s been after me. moss: What, Hawkshaw, the ’cutest detective in the force.
[US]A.J. Pollock Und. Speaks n.p.: Nailer, a uniformed police officer.
[US]C. Cooper Jr Scene (1996) 308: Nailers: police.
[US] ‘Railroads have “Slanguage”’ in Newark (OH) Advocate 21 May 3/3–4: nailer – a railroad detective.

3. an extreme example, whether good or bad; applied to people, animals or objects.

[Aus]Bell’s Life in Sydney 1 Sept. 3/2: One Joseph Housley, a nailer (a dead nailer), of Sussex streot, and a very old sinner beside.
[UK]Marshall ‘Pomes’ from the Pink ’Un 88: At guzzling the whole lot were nailers [F&H].
[UK]Sporting Times 3 May 3/1: My! She is a nailer, and such diamonds.
[UK][perf. Lottie Collins] A Leader of Society [lyrics] Well, I'm Missis Talbot Taylor, a regular, right down nailer.
[NZ]H.B. Vogel Maori Maid 150: She’s a perfect nailer! She’s one of the prettiest girls I’ve ever seen.

4. a severe blow.

[UK]Westmorland Gaz. 7 May 5/5: One of the ‘boys’ gave Billy such a nailer with his shillalah on the back side of his head that Billy was nailed to his mother earth.

5. an extortionist.

[UK]Illus. London News Summer No.26 3: The Stomach of the Bar, collective and individual, is revolted and scandalised at the idea of its members doing anything for nothing. Yes, put in Eustace, I have always understood that they were regular nailers [F&H].