Organ used by sea rangers (3)
I believe the answer is:
ear
'organ' is the definition.
(ear is a kind of organ)
'used by sea rangers' is the wordplay.
'used by' indicates a hidden word.
'EAR' is hidden within 'sea rangers'.
(Other definitions for ear that I've seen before include "Seed-bearing part of corn" , "That makes sense" , "willingness to listen" , "Shell-like; corn" , "Go astray" .)