Becoming aware of frost having melted? (8)
I believe the answer is:
noticing
'becoming aware of' is the definition.
(I've seen this before)
'frost having melted?' is the wordplay.
I cannot quite see how this works, but
'frost' could be 'icing' (synonyms) and 'icing' is found within the answer.
The remaining letters 'not' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for noticing that I've seen before include "Perceiving" , "Spotting" , "Observing" , "Seeing, detecting" , "Becoming aware of" .)