A person who complains a lot and is often in a bad mood; someone who is grumpy.
Likely from a combination of 'grum' (morose, surly, from 16th century) and 'bump' or related to 'groan.' It became more common in the 20th century.
The word 'grump' gained popularity through Oscar the Grouch on Sesame Street, and now it's used affectionately to describe anyone who seems cranky—even though grumpy people are often just having a bad day!
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