Roughly means to restrain a matelot (6)
I believe the answer is:
seaman
'matelot' is the definition.
(thesaurus)
'roughly means to restrain a' is the wordplay.
'roughly' indicates an anagram.
'to restrain' means one lot of letters goes inside another.
'means' is an anagram of 'seamn'.
'seamn' going around 'a' is 'SEAMAN'.
(Other definitions for seaman that I've seen before include "A manse (anag.)" , "Mariner" , "Sailor" , "crew member" .)