To be silent, moody, and bad-tempered, usually because you're upset or angry about something.
Origin uncertain, possibly from Scandinavian languages. First appeared in English in the late 1700s, possibly related to an obsolete word 'sulke' meaning 'to lurk' or 'to lie in ambush.'
Sulking is one of the few emotions that's entirely performative—you need an audience to notice you're upset, which is why kids sulk around parents but not when they're alone. The word might originally have meant 'to lurk,' suggesting someone withdrawing from sight to be noticed by their absence.
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