Classy headgear, an ideal (7)
I believe the answer is:
utopian
'ideal' is the definition.
(similar in meaning)
'classy headgear an' is the wordplay.
'classy' becomes 'u' (I've seen this in other clues).
'headgear' becomes 'topi' (topi is a kind of headgear).
'u'+'topi'+'an'='UTOPIAN'
(Other definitions for utopian that I've seen before include "Fantastic" , "Unworkable" , "Impractically idealistic" , "I put on a show of perfect kind" , "in a dreamy state" .)