gilhickie, n. — Green’s Dictionary of Slang

gilhickie n.

also gilhickey

[naut. use gilguy, a gadget + dohickey n.¹]

anything for which one has forgotten the name.

1922		Leatherneck 22 Apr. 5: Gil-hickey: A gadget [HDAS].
1944		P. Kendall Dict. Service Sl. n.p.: gilgadget . . . a gilhickey or a gimmick or a gadget.