American leader's pretty perceptive (5)
I believe the answer is:
acute
'perceptive' is the definition.
(similar in meaning)
'american leader's pretty' is the wordplay.
'leader' indicates taking the first letters.
'pretty' becomes 'cute' (both can mean attractive).
The initial letter of 'american' is 'a'.
'a'+'cute'='ACUTE'
(Other definitions for acute that I've seen before include "(Of an angle) less than 90deg" , "Piercing" , "Excruciating" , "Canny" , "Discerning" .)