Popular number two's first aim (6)
I believe the answer is:
intent
'aim' is the definition.
('intent' can be a synonym of 'aim')
'popular number two's first' is the wordplay.
'popular' becomes 'in'.
'number' becomes 'ten' (ten is a kind of number**).
'first' indicates taking the first letters.
The first letter of 'twos' is 't'.
'in'+'ten'+'t'='INTENT'
(Other definitions for intent that I've seen before include "Mean to" , "wrapped up" , "Bent on, determined to" , "7 Purpose; fixed (upon)" , "Firm - plan - steadfast - purpose" .)