Green’s Dictionary of Slang

(N.Z./US) any small, otherwise nameless object; occas. an unknown person.

1903		Ade People You Know 112: He heard a Hickey in a Striped Sweater tell a red-headed Man that [etc.].
1907		C. Fowler letter 22 Jan in Tomlinson Rocky Mountain Sailor (1998) 202: I am pleased to hear that you received all of the hickies, but I'm afraid that there was one parcel that went astray. It was another set of those napkin rings .
1913		‘Terms From Tennessee’ in DN IV:i 58: hickey, n. Thing [...] ‘Hand me that hickey.’.
1938		D. Runyon ‘The Big Umbrella’ in Runyon on Broadway (1954) 551: The hotel [...] puts a hickey in his keyhole and now he cannot get at his other clothes.
1988		McGill Dict. of Kiwi Sl. 56/1: hickey [...] thingummygig, late C19.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].