React fearfully to the cold? (6)

I believe the answer is:

shiver

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'react' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how one could define the other.

I can't explain the remainder of the clue.

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(Other definitions for shiver that I've seen before include "Smash; tremble" , "Momentary tremble" , "Shake (with cold, excitement etc)" , "Slightly shake" , "Shake uncontrollably" .)

I've seen this clue in the Evening Standard.

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