Seen but not frozen (7)
I believe the answer is:
noticed
'seen' is the definition.
(I've seen this before)
'not frozen' is the wordplay.
'frozen' becomes 'iced' (I've seen this before).
'not'+'iced'='NOTICED'
'but' acts as a link.
(Other definitions for noticed that I've seen before include "Seen" , "Marked" , "remarked" , "Detected" , "Became aware of" .)