John can act with melting effect (4)

I believe the answer is:

thaw

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'melting effect' is the definition.
'thaw' can be an answer for 'melting' (thesaurus). I am unsure of the 'effect' bit.

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

Can you help me to learn more?

(Other definitions for thaw that I've seen before include "Unfreeze, defrost" , "when the temperature rises?" , "As Lewis's boss, you'll have seen me" , "detente" , "Become warmer" .)

I've seen this clue in the Evening Standard.

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