Reflection, but only half of it (7)
I believe the answer is:
thought
'reflection' is the definition.
(I've seen this before)
'but only half of it' is the wordplay.
'but' becomes 'though' (I've seen this before).
'only half of' suggests halving the letters.
'it' cut in half is 't'.
'though'+'t'='THOUGHT'
(Other definitions for thought that I've seen before include "Cogitation" , "Content of cognition" , "Thinking process" , "Idea, opinion" , "Philosopher must master this" .)