I see mariner's brought round cutter (6)
I believe the answer is:
tailor
'cutter' is the definition.
(cutter can mean a tailor)
'i see mariner's brought round' is the wordplay.
'see' becomes 'lo' (archaic word meaning 'look!').
'mariner' becomes 'tar' (synonyms).
'brought round' is an insertion indicator.
'i'+'lo'='ilo'
'ilo' put inside 'tar' is 'TAILOR'.
(Other definitions for tailor that I've seen before include "person before soldier and sailor in list" , "Outfitter" , "Clothes-maker" , "Garment maker" , "man of the cloth" .)