Green’s Dictionary of Slang

1. a cheat, an imposter.

1756		W. Toldervy Hist. of the Two Orphans I 70: Tom was one of those numerous hummers, that if one good thing escapes them, are sure to destroy it with five or six bad ones.
c.1778		H. Brooke ‘On Humbugging’ in Chalmers Eng. Poets XVII (1810) 428/1: But, what are all hummers, their tricks and their arts, To yon roguish round, the humbuggers of hearts [...] For beauty, by ancient tradition, we find, Has delightfully humm’d the whole race of mankind.
1900		Nat. Police Gaz. (NY) 14 July 6/1: [headline] this dainty soubrette / Was A Hummer, You Bet, And She / turned a town topsy-turvy / She Was Wanted in Jail, but Her ‘Papa Gave Bail; Then She Played Him a Trick That Was Scurvy.

2. (US black) something deceptive, a minor or insignificant mistake.

1959		Esquire Nov. 70I: hummer: a minor mistake, something that shouldn’t have happened.
1961		Rigney & Smith Real Bohemia 167: I was caught off guard, but that’s the way the man shows, on a hummer when you least expect it.
1967		M. Braly On the Yard (2002) 201: ‘It [i.e. the report of an escape] was a hummer,’ the captain said. ‘I know, Jake, the duty officer told me.’.
1971		H.E. Roberts Third Ear n.p.: hummer n. 1. a nothing person. 2. an unimportant or insignificant event.