To make someone dissatisfied, annoyed, or discontented; to upset someone's mood or feelings.
From dis- (to reverse or negate) + gruntle (back-formed from 'disgruntle' itself, from Middle English grunten, 'to grunt'). Gruntle seems related to grunt, suggesting quiet grumbling sounds of dissatisfaction.
This word is special because 'gruntle' doesn't really exist on its own—'disgruntle' is so old that we had to invent 'gruntle' backwards from it, making it one of English's accidental auto-antonyms.
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