End sadly involved swallowing one's pride? (6,3)
I believe the answer is:
deadly sin
'pride?' is the definition.
(pride is a kind of deadly sin)
'end sadly involved swallowing one's' is the wordplay.
'involved' indicates an anagram (involved can mean confusing or complex).
'swallowing' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'end'+'sadly'='endsadly'
'endsadly' is an anagram of 'deadlysn'.
'deadlysn' going around 'i' is 'DEADLY SIN'.
(Other definitions for deadly sin that I've seen before include "Greed, perhaps" , "Eg, lust or pride" , "not good - bad" , "Anger, covetousness, envy, gluttony, lust, pride or sloth" , "greed, or lust" .)