Standard spare part (3)
I believe the answer is:
par
'standard' is the definition.
(thesaurus)
'spare part' is the wordplay.
'part' indicates a hidden word.
'PAR' is hidden in the letters of 'spare'.
(Other definitions for par that I've seen before include "A number of golfing" , "Standard score for golfers" , "Regular score" , "Average standard" , "Normal level or standard" .)