Second character surviving flood is a fraud (4)
I believe the answer is:
sham
'fraud' is the definition.
(synonyms)
'second character surviving flood' is the wordplay.
'second' becomes 's' (common abbreviation).
'character surviving flood' becomes 'Ham' (a son of Noah in the Bible).
's'+'ham'='SHAM'
'is a' acts as a link.
(Other definitions for sham that I've seen before include "Feign" , "Cheap falseness" , "Phoney, bogus" , "False and phoney" , "Phoney sort of hams" .)