Sailor one eating a large snail (7)
I believe the answer is:
abalone
'large snail' is the definition.
(I've seen this in another clue)
'sailor one eating a' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'one eating' becomes 'al' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a' becomes 'one'.
'ab'+'al'+'one'='ABALONE'
Can you help me to learn more?
(Other definitions for abalone that I've seen before include "produces an ear shell" , "Source of mother-of-pearl" , "Shell used for decoration" , "paua" , "gastropod" .)