Green’s Dictionary of Slang

(N.Z.) an otherwise nameless object, often a gadget.

c.1945		Sixes and Sevens (Troopship pub.) 7: ‘My oath,’ I said. ‘Many a Jap binjie is going to get a hoodickey stuck in it before sparrow-hiccough.’ [DNZE].
1955		B.J. Cameron Collection in DNZE (1998) 357/2: hoojacky (n) f Thingummy.
1988		McGill Dict. Kiwi Sl. 51/2: hoodackie thingummygig; variant of ‘doodackie’.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].