Bad month I confess, initially (6)
I believe the answer is:
septic
'bad' is the definition.
(thesaurus)
'month i confess initially' is the wordplay.
'month' becomes 'sept' (I've seen this before**).
'initially' says to take the initial letters.
The initial letter of 'confess' is 'c'.
'sept'+'i'+'c'='SEPTIC'
(Other definitions for septic that I've seen before include "Type of tank" , "Of wound, infected with pus" , "Caused by putrefaction" , "Infected with bacteria" , "Putrefactive" .)