Green’s Dictionary of Slang

grooly adj.

[SE gru(esome) + (gris)ly]

sinister.

1934		R. Knox Still Dead n.p.: Dashed cowardly of me, but . . . It’s just the tinest bit grooly, isn’t it?
1937–84		Partridge DSUE (1984) 506/2: from ca. 1920.