More crabby or grumpy; having a more irritable or bad-tempered disposition.
From 'crabby' (English, 16th century, from crab apple which is sour) plus the comparative suffix '-er'. The connection between crabs' sideways movement and grumpiness is folk etymology.
Crabby doesn't actually come from the animal's behavior—it comes from crab apples, which are extremely sour! Medieval people associated sourness with grumpiness, creating a metaphor that stuck for 400 years.
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