End of first-class male (3)
I believe the answer is:
aim
'end' is the definition.
(I've seen this before)
'first-class male' is the wordplay.
'first class' becomes 'ai' (A1 - top quality).
'male' becomes 'm' (common abbreviation).
'ai'+'m'='AIM'
'of' is the link.
(Other definitions for aim that I've seen before include "anticipated" , "Object; intend" , "Set sights on, target or goal" , "This is mean" , "Plan" .)