Bending or hanging downward in a sad or tired way; present participle of droop.
From Old Norse 'drūpa' meaning to droop or hang down. The word entered Middle English through Scandinavian influence and has kept its meaning of hanging downward for over 1000 years.
The word 'droop' is onomatopoetic-adjacent—while it's not a sound effect, it actually sounds like what it means because of the 'oo' sound in the middle that makes your mouth kind of hang open the way drooping things hang down.
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