Green’s Dictionary of Slang

1. (US) slimy, sticky, dirty viscid matter, also distasteful food.

1942		Berrey & Van den Bark Amer. Thes. Sl.
1958		Mad mag. Jul.–Aug. n.p.: The whole pie will fall apart [...] getting icky sticky gook all over your new [...] suit.
1965		L. Bruce How to Talk Dirty 131: He [...] smeared gook on my face.
1975		H. Ellison ‘Along the Scenic Route’ in Deathbird Stories (1978) 40: The Merc sprayed JP-4 gook and water in a wide fan from its jet nozzle.
1986		S. King It (1987) 299: The gook in between the two boards will take most of the water pressure.
1992		M. Leyner Et Tu, Babe (1993) 101: I don’t want a President who wakes up with green gook in his eyes, all groggy.

2. (US) anything unpleasant; nonsense.

1960		G. Swarthout Where the Boys Are 150: I think all that gook is self-evident.
1961		F. Kohner Gidget Goes Hawaiian 63: He was full of gook, that Pete.
1970		‘Troy Conway’ Cunning Linguist (1973) 56: You mustn’t believe all that good gook about stews, anyway. Some of them can be as prim and spinsterish as a Geraldine Page movie.