Relish pertness (5)
I believe the answer is:
sauce
This clue is a double definition.
'relish' is the first definition.
(I've seen this before)
'pertness' is the second definition.
(thesaurus)
(Other definitions for sauce that I've seen before include "sharp language" , "Cranberry or brandy, say" , "Relish or impertinence" , "Cause for relish" , "Dressing served with food" .)