Almost frozen stream perhaps showing eventual strong response (4,4)
I believe the answer is:
slow burn
'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".)