This word is glossed “grey” in The Etymologies, but perhaps means “✱foggy, overcast”, since Sindarin cognate hethw means “foggy, obscure, vague” and related noun hiswë means “fog”. @@@
Qenya
mista-
verb. to stray about
hiswa
adjective. grey, grey [of weather], *foggy, overcast; [ᴱQ.] dim, fading
A verb in The Etymologies of the 1930s glossed “stray about” derived from the root ᴹ√MIS “go free, stray, wander” (Ety/MIS).