Green’s Dictionary of Slang

sharp n.1

[sharp v.; note shop assistants’ jargon Mr Sharp, a known shoplifter or fraud]

1. [late 18C+] (UK Und.) a confidence trickster.

2. [19C–1920s] an expert or connoisseur, a clever person or one who poses as such; also, in comb. with n., a job title, e.g. doctor sharp, revenue sharp.

3. in pl., from medical jargon sharps, needles, scalpels etc.

(a) [1900s–30s] household needles.

(b) [1980s+] (drugs) hypodermic needles.

4. [1960s] (US campus) an attractive and/or socially adept person.

In phrases

book sharp (n.)

[late 19C] (US, Western) an intellectual.

horse sharp (n.)

[mid-19C] (US) a crooked racecourse gambler.

on the sharp

1. [18C] fraudulently.

2. [mid-18C–19C] attempting to defraud victims; thus go on the sharp(s).

3. [mid-19C] (UK Und.) too alert to be easily cheated.

weather sharp (n.)

[late 19C–1950s] (US) a weather-forecaster.