Ideal cover secured by upper-class Scotsman (7)
I believe the answer is:
utopian
'ideal' is the definition.
(similar in meaning)
'cover secured by upper-class scotsman' is the wordplay.
'cover' becomes 'top' (synonyms).
'secured by' means one lot of letters goes inside another (I've seen this in other clues).
'upper-class' becomes 'u' (similar in meaning).
'scotsman' becomes 'ian'.
'u'+'ian'='uian'
'top' going within 'uian' is 'UTOPIAN'.
(Other definitions for utopian that I've seen before include "Fantastic" , "in a dreamy state" , "Too perfect for this world" , "Thomas More-ish?" , "I put on a show of perfect kind" .)