Sailor has name for mountain lake (4)
I believe the answer is:
tarn
'mountain lake' is the definition.
(I've seen this before)
'sailor has name' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'has' means one lot of letters go next to another.
'name' becomes 'n' (common abbreviation e.g. on forms).
'tar'+'n'='TARN'
'for' is the link.
(Other definitions for tarn that I've seen before include "Small mountain lake" , "Mountain pool: French department" , "Scottish mountain lake" , "High water" .)