Sailor to attain goal (6)
I believe the answer is:
target
'goal' is the definition.
(target is a kind of goal)
'sailor to attain' is the wordplay.
'sailor' becomes 'tar' (tar can mean a sailor).
'to attain' becomes 'get' (I've seen this in another clue).
'tar'+'get'='TARGET'
(Other definitions for target that I've seen before include "purpose" , "Fixed goal" , "Object to be attained by archers (or fund raisers?)" , "The object with the bullseye" , "Reference point to shoot at" .)