Thought end of carol perfect (5)
I believe the answer is:
ideal
'perfect' is the definition.
('ideal' can be similar in meaning to 'perfect')
'thought end of carol' is the wordplay.
'thought' becomes 'idea' ('idea' can be a synonym of 'thought'**).
'end of' suggests the final letters.
The last letter of 'carol' is 'l'.
'idea'+'l'='IDEAL'
(Other definitions for ideal that I've seen before include "Model of excellance" , "Perfectly suited" , "Embodying perfection" , "Standard to aim for" , "Benchmark" .)