Peer brought up in case: most amusing (8)
I believe the answer is:
drollest
'most amusing' is the definition.
(droll can mean amusing or comical)
'peer brought up in case' is the wordplay.
'peer' becomes 'lord' (lord is a type of peer).
'brought up' is a reversal indicator (in a down clue, letters go up).
'in case' becomes 'lest' (eg 'lest we forget').
'lord' reversed gives 'drol'.
'drol'+'lest'='DROLLEST'
(Other definitions for drollest that I've seen before include "most amusing" , "Most diverting" .)