Crossword Genius

Almost frozen stream perhaps showing eventual strong response (4,4)

Ross

I believe the answer is:

slow burn

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'perhaps showing eventual strong response' is the definition.
I can't judge whether this definition defines the answer.

'almost frozen stream' is the wordplay.
'almost frozen' becomes 'slow' (I can't justify this - if you can you should give a lot more credence to this answer).
'stream' becomes 'burn' (a burn is a small stream).
'slow'+'burn'='SLOW BURN'

Can you help me to learn more?

(Another definition for slow burn that I've seen is " Delayed but finally strong reaction".)

I've seen this clue in The Independent.
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