Green’s Dictionary of Slang

fan v.1

[SE fan, to wave a fan]

1. [late 18C+] (US 20C+) to beat; also in fig. use, as in excl. fan my jawbone! [underpinned by SE fan, to winnow or thresh corn].

2. [mid-19C+] to run one’s hands over a potential victim’s clothes to see if they have anything in their pockets that can be stolen; thus fan out of v., to steal while ‘fanning’ [poss. link to fam v.].

3. [1910s+] (orig. US) to conduct a search of a suspect’s clothes, possessions or premises [poss. link to fam v.].

4. [1920s+] (also give the fan) to pick pockets [poss. link to fam v.].

5. [1930s] to shoot.

In phrases

cross-fanner (n.)

[late 19C] a variety of pickpocket who works by running their hands over the victim’s clothing.

SE in slang uses

In phrases

fan the hammer (v.) [the action of fanning the hammer of a pistol or revolver in order to fire more speedily]

[late 19C] (US) to act in a brilliant but unscrupulous manner.