Gloom is defined as darkness or a dark and gloomy place, or it is defined as a state of being depressed and in a bad mood.(noun)
The definition of gloom is to feel or act sad.(verb)
An example of gloom is to become very sad with the death of a friend.
See gloom in Webster's New World College Dictionary
Origin: < ME gloum(b)en, to look morose, prob. < Scand, as in Norw dial. glome, to stare somberly, akin to EFris glumen, to peer secretly (< IE *ĝhlu- < base *ghêl- > gleam, glow): meaning infl. by OE glom, twilight
See gloom in American Heritage Dictionary 4
Origin: Probably from Middle English gloumen, to become dark, look glum.
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