KC (second class) (4)
I believe the answer is:
silk
'kc' is the definition.
(thesaurus)
'second class' is the wordplay.
'second' becomes 's' (common abbreviation).
'class' becomes 'ilk' (both can mean a type or variety).
's'+'ilk'='SILK'
(Other definitions for silk that I've seen before include "it's taken by QC" , "Glossy fibre" , "Superior barrister" , "Advocate" , "Item of fine legwear" .)