This class is certain to be kept in idle fashion (8)
I believe the answer is:
leisured
'this class' is the definition.
The definition and answer are not the same part of speech.
'certain to be kept in idle fashion' is the wordplay.
'certain' becomes 'sure' (synonyms).
'to be kept in' is an insertion indicator.
'fashion' indicates anagramming the letters.
'idle' is an anagram of 'leid'.
'sure' placed inside 'leid' is 'LEISURED'.
'is' is the link.
Can you help me to learn more?
(Other definitions for leisured that I've seen before include "unhurried" , "Having plenty of free time" , "Having much free time" , "Not needing to work" .)