Large individual, Edward VII acquiring name as this (9)
I believe the answer is:
Here is my best explanation:
'this' is the definition.
The definition suggests a singular noun which matches the answer.
'large individual edward vii acquiring name' is the wordplay.
'large' becomes 'l'.
'individual' becomes 'i'.
'edward vii' becomes 'bertie' (nickname of Edward VII, born Albert).
'acquiring' means one lot of letters goes inside another.
'name' becomes 'n' (common abbreviation e.g. on forms).
'bertie' placed around 'n' is 'bertine'.
'as' acts as a link.
(Other definitions for libertine that I've seen before include "Morally dissolute", "of roues", "Say, Don Giovanni", "Rakish", "Don Giovanni, say", "Debauchee", "reprobate", "Sensually indulgent person", "Rake" and "Rou".)