Old sailor that barnacle clings to? (4)
I believe the answer is:
salt
'old sailor' is the definition.
(old-fashioned nickname for a sailor)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for salt that I've seen before include "Brackish" , "dry wit" , "Sea dog" , "Seasoned sailor" , "White crystalline substance" .)