Sailor needing to achieve objective (6)
I believe the answer is:
target
'objective' is the definition.
('target' can be a synonym of 'objective')
'sailor needing to achieve' is the wordplay.
'sailor' becomes 'tar' (tar is a kind of sailor).
'needing' says to put letters next to each other.
'to achieve' becomes 'get'.
'tar'+'get'='TARGET'
(Other definitions for target that I've seen before include "Fixed goal" , "bull's eye" , "Aim, objective" , "Goal, objective" , "Aim, ambition" .)