Rob set out for some water-ice (6)
I believe the answer is:
sorbet
'some water-ice' is the definition.
(I've seen this before)
'rob set out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'rob'+'set'='robset'
'robset' anagrammed gives 'SORBET'.
'for' acts as a link.
(Other definitions for sorbet that I've seen before include "Refresher course" , "Strobe (anag.)" , "Water ice dessert" , "Fruit water-ice" , "Water ice to cleanse the palate" .)