Sailor to achieve aim (6)
I believe the answer is:
target
'aim' is the definition.
(both can mean a goal or purpose)
'sailor to achieve' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'to achieve' becomes 'get' (I've seen this in another clue).
'tar'+'get'='TARGET'
(Other definitions for target that I've seen before include "Butt" , "Aim of an attack" , "Thing aimed at" , "Aim, ambition" , "Reference point to shoot at" .)