Inept don messed up conclusion (8)
I believe the answer is:
endpoint
'up conclusion' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'inept don messed' is the wordplay.
'messed' is an anagram indicator (letters get messed up).
'inept'+'don'='ineptdon'
'ineptdon' is an anagram of 'ENDPOINT'.
Can you help me to learn more?
(Other definitions for endpoint that I've seen before include "The last bit" , "goal" .)