Think deeply about mirror (7)
I believe the answer is:
reflect
This clue could be a double definition.
'think deeply' is the first definition.
'reflect' can be an answer for 'think' (reflecting is a kind of thinking). I am not sure about the 'deeply' bit.
'mirror' is the second definition.
(mirror can mean to reflect)
'about' acts as a link.
Can you help me to learn more?
(Other definitions for reflect that I've seen before include "Contemplate like mirror" , "'Ponder, chew over (7)'" , "Ponder; send back" , "Think - what mirrors do" , "Ponder, contemplate" .)