Mirror leader utilised reflected (5)
I believe the answer is:
mused
'reflected' is the definition.
('muse' can be a synonym of 'reflect')
'mirror leader utilised' is the wordplay.
'leader' says to take the initial letters.
'utilised' becomes 'used' (similar in meaning).
The initial letter of 'mirror' is 'm'.
'm'+'used'='MUSED'
(Other definitions for mused that I've seen before include "Closer" , "Was absorbed in thought" , "Thought (to oneself)" , "Reflected or pondered" , "'Meditated, mulled (5)'" .)