In a state of rapid vibration or trembling; jittery or nervous.
From English 'a-' (in a state of) plus 'jitter', combining Old English prefix patterns with the modern colloquial 'jitter' (from uncertain origin, possibly imitative). Created in American English as an informal adjective.
The 'a-' prefix is a ghost of Old English—when you say someone is 'ajitter' you're using medieval grammar patterns to describe modern anxiety, making ancient language describe our modern nervous world.
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