Debate socially acceptable in appearance (5)
I believe the answer is:
forum
'debate' is the definition.
(thesaurus)
'socially acceptable in appearance' is the wordplay.
'socially acceptable' becomes 'u'.
'in' means one lot of letters goes inside another.
'appearance' becomes 'form' (form is a kind of appearance).
'u' inserted within 'form' is 'FORUM'.
(Other definitions for forum that I've seen before include "Tribunal" , "Meeting of people for discussion" , "Internet message board" , "Court - conference" , "Place to discuss ideas" .)