Barbarian cut grass back, round and round (5)
I believe the answer is:
yahoo
'barbarian' is the definition.
(thesaurus)
'cut grass back round and round' is the wordplay.
'cut grass' becomes 'hay' (I've seen this before).
'back' shows that the letters should be reversed in order.
'round' becomes 'o' (o is a circular letter).
'and' says to put letters next to each other.
'round' becomes 'o' (o is a circular letter).
'hay' reversed gives 'yah'.
'yah'+'o'+'o'='YAHOO'
(Other definitions for yahoo that I've seen before include "expression of delight" , "Boorish louts" , "One of Dean Swift's brute people" , "Rude or coarse person" , "[WHOOPEE] !" .)