/ ˈsʌlən; NAmE / adjective ( disapproving )
1.
bad-tempered and not speaking, either on a particular occasion or because it is part of your character :
Bob looked pale and sullen.
She gave him a sullen glare.
sullen teenagers
2.
( literary ) ( of the sky or weather ) dark and unpleasant
► sul·len·ly adverb
► sul·len·ness noun [ U ]
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WORD ORIGIN
Middle English (in the senses solitary, averse to company , and unusual ): from Anglo-Norman French sulein , from sol sole.