In a jiffy, giving you a synonym for "wobbly" (6)

I believe the answer is:

ashake

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'in' is the definition.
Both the answer and definition are adjectives.
Perhaps you can see a link between them that I don't see?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for ashake that I've seen before include "Trembling" , "Vibrating" .)

I've seen this clue in the Evening Standard.

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