Thought leading lady perfect (5)
I believe the answer is:
ideal
'perfect' is the definition.
('ideal' can be similar in meaning to 'perfect')
'thought leading lady' is the wordplay.
'thought' becomes 'idea' ('idea' can be a synonym of 'thought'**).
'leading' says to take the initial letters.
The initial letter of 'lady' is 'l'.
'idea'+'l'='IDEAL'
(Other definitions for ideal that I've seen before include "To which one aspires" , "Optimal" , "Perfectly suited" , "Standard of perfection or excellence" , "Paragon" .)