Visitor called cutting rest, unfortunately (8)
I believe the answer is:
stranger
'visitor' is the definition.
(thesaurus)
'called cutting rest unfortunately' is the wordplay.
'called' becomes 'rang' ('ring' can be a synonym of 'call').
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'unfortunately' indicates anagramming the letters.
'rest' with letters rearranged gives 'ster'.
'rang' going inside 'ster' is 'STRANGER'.
(Other definitions for stranger that I've seen before include "visitor" , "'Fact is ........ than fiction'" , "Alien; odder" , "'Weirder, odder (8)'" , "Person in place or company to which he does not belong" .)