Head of glamour girl in 'Mirror'? (5)
I believe the answer is:
glass
''mirror'?' is the definition.
(glass is a kind of mirror)
'head of glamour girl' is the wordplay.
'head of' indicates taking the first letters.
'girl' becomes 'lass' (lass is a kind of girl**).
The initial letter of 'glamour' is 'g'.
'g'+'lass'='GLASS'
'in' is the link.
(Other definitions for glass that I've seen before include "Translucent, usually transparent, material" , "Calm lake may be compared to this" , "Vitreous material" , "barometer" , "Telescope perhaps" .)