Green’s Dictionary of Slang

nab n.1

also nabe
[ety. unknown; ? link to dial. nab, a projecting lump of rock, a promontory]

1. [mid-16C–17C] (UK Und.) the head.

2. [early 17C] (UK Und.) the head of a stick or penis.

3. [early 17C–mid-19C] (UK Und.) a hat.

4. [late 17C–mid-18C] (UK Und.) a coxcomb, a fop.

5. [early 19C] (UK Und.) an important person.

6. [1990s+] (Irish) the devil.

7. [1990s+] (Irish) the joker (cards).

In compounds

nab cheat (n.) (also nabchet, nob chete) [cheat n. (1)]

[16C–early 19C] (UK Und.) a hat, a cap.

nab girder (n.) (also nab garder, nob girder) [SE gird]

[late 17C–mid-19C] (UK Und.) a bridle.

In phrases

nabs on (adj.)

[late 19C] (UK Und.) signifying the hallmark, i.e. proof of quality, on a silver or gold object.