Mop Cornish sailor used? (4)
I believe the answer is:
swab
'mop' is the definition.
(synonyms)
'cornish sailor used?' is the wordplay.
I cannot quite understand how this works, but
'cornish' could be 'sw' (Cornwall is in the South West of England) and 'sw' is found within the answer.
'sailor' could be 'ab' (abbreviation for able seaman) and 'ab' is present in the answer.
No letters remain.
This explanation may well be incorrect...
(Other definitions for swab that I've seen before include "Wound-cleaner" , "Absorbent pad for cleansing or drying" , "Cloth for cleaning wounds" , "Among others, Q-tip" , "Pad used in surgery" .)