All 3 Uses

ominous
in
The Hobbit
(Auto-generated)

Great floods and rains had swollen the waters that flowed east; and there had been an earthquake or two (which some were inclined to attribute to the dragon-alluding to him chiefly with a curse and an ominous nod in the direction of the Mountain).†
p. 175.2

ominous = threatening (suggestive of, or foreshadowing bad things to come)
Nothing moved in the waste, save the vapour and the water, and every now and again a black and ominous crow.†
p. 189.3
...they looked seldom at it, for it was ominous and dreary even in the light of morning.
p. 225.5 *

ominous = suggestive of evil or something bad

Definitions: