Title held by the Mirror? (4)
I believe the answer is:
emir
'title' is the definition.
(I have seen 'Islamic title ' mean 'emir' so perhaps 'title' could also mean 'emir')
'held by the mirror?' is the wordplay.
'held by' says the answer is hidden in the clue.
'EMIR' can be found hidden inside 'the mirror'.
(Other definitions for emir that I've seen before include "eader abroad?" , "Islamic ruler" , "Islamic title" , "Muslim ruler stuck in mire" , "Arab ruler" .)