Paul’s friend foolishly admitting one revealing lapse (8,4)
I believe the answer is:
freudian slip
'lapse' is the definition.
Both the definition and answer are singular nouns.
Maybe you can see a link between them that I can't see?
'paul's friend foolishly admitting one' is the wordplay.
'foolishly' indicates anagramming the letters.
'admitting' means one lot of letters goes inside another (admit can mean to welcome in or accept).
'one' becomes 'i' (Roman numeral).
'pauls'+'friend'='paulsfriend'
'paulsfriend' anagrammed gives 'freudanslip'.
'freudanslip' going around 'i' is 'FREUDIAN SLIP'.
'revealing' is the link.
Can you help me to learn more?
(Other definitions for freudian slip that I've seen before include "Spoken error revealing unconscious thought" , "can be a revealing thing" , "Unintentional error" , "Mistake revealing hidden concerns" , "Words revealing unconscious thoughts" .)