Sailor has to acquire aim (6)
I believe the answer is:
target
'aim' is the definition.
('target' can be a synonym of 'aim')
'sailor has to acquire' is the wordplay.
'sailor' becomes 'tar' (tar is a kind of sailor).
'has' is a charade indicator (letters next to each other).
'to acquire' becomes 'get' ('get' can be a synonym of 'acquire').
'tar'+'get'='TARGET'
(Other definitions for target that I've seen before include "Object to be aimed at" , "'Aim, goal (6)'" , "Aim, objective" , "Aim of an attack" , "Goal to be aimed for" .)