Foot of column found beneath salt lake (4)
I believe the answer is:
tarn
'lake' is the definition.
(I know that tarn is a type of lake)
'foot of column found beneath salt' is the wordplay.
'foot of' indicates one should take the final letters.
'found beneath' means one lot of letters go next to another (I've seen this in other clues).
'salt' becomes 'tar' (both can informally mean a sailor).
The final letter of 'column' is 'n'.
'n' after 'tar' is 'TARN'.
(Other definitions for tarn that I've seen before include "Small mountain lake" , "Mountain pool: French department" , "High water" , "Scottish mountain lake" .)