Baptism misrepresented in memoirs (9)
I believe the answer is:
immersion
'baptism' is the definition.
(I know that immersion is a type of baptism)
'misrepresented in memoirs' is the wordplay.
'misrepresented' indicates anagramming the letters.
'in'+'memoirs'='inmemoirs'
'inmemoirs' is an anagram of 'IMMERSION'.
(Other definitions for immersion that I've seen before include "dip" , "Deep absorption; baptism" , "Baptism; deep involvement" , "Deep absorption (in a subject)" .)