Green’s Dictionary of Slang

nap n.1

[lit. and fig. uses of nap v.1 ]

1. a dose of venereal disease.

[UK]B.E. Dict. Canting Crew n.p.: Nap [...] a Clap, or Pox.
[UK]New Canting Dict. [as cit. c.1698].
[UK]Bailey Universal Etym. Eng. Dict. [as cit. c.1698].

2. an instance of cheating while playing dice.

[UK]B.E. Dict. Canting Crew n.p.: Nap, c. Nap, by Cheating with the Dice to secure one Chance.

3. (orig. theatre) a blow or hit, esp. a pretend hit.

[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor III 129/1: I give him the ‘nap,’ and knock him on his back.

In phrases