adj
bats
bats
adj
1
Informal: crazy or mentally unstable.
"He's gone completely bats since the divorce."
How to Use Bats
Learner’s notesIn plain EnglishAn informal way of calling someone or something crazy.
When to use it
Informal/dated — you'll hear it more in older British writing than everyday modern speech.
Easily confused with
Word Forms
more bats comparative, most bats superlative
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He's gone completely _____ since the divorce.
Etymology
From "bat(man)" plus the hypocoristic -s ending, likely reinforced by the phrase "bats in the belfry."