Sailor has name for lake (4)
I believe the answer is:
tarn
'lake' is the definition.
(tarn is a kind of lake)
'sailor has name' is the wordplay.
'sailor' becomes 'tar' (tar is a kind of sailor).
'has' is a charade indicator (letters next to each other).
'name' becomes 'n' (common abbreviation e.g. on forms).
'tar'+'n'='TARN'
'for' acts as a link.
(Other definitions for tarn that I've seen before include "Mountain pool: French department" , "Scottish mountain lake" , "High water" , "Small mountain lake" .)