Mean to be a first-class leader of men (3)
I believe the answer is:
aim
'mean' is the definition.
(aiming is a kind of meaning)
'a first-class leader of men' is the wordplay.
'a first class' becomes 'ai' (A1 - top quality).
'leader of' indicates taking the first letters.
The initial letter of 'men' is 'm'.
'ai'+'m'='AIM'
'to be' is the link.
(Other definitions for aim that I've seen before include "mission" , "Ambition or goal" , "anticipated" , "Object; intend" , "road?" .)