May include a witticism for ‘splendour’ (7)
I believe the answer is:
majesty
'splendour' is the definition.
(I've seen this before)
'may include a witticism' is the wordplay.
'include' means one lot of letters goes inside another.
'a witticism' becomes 'jest' (jest is a kind of witticism).
'may' enclosing 'jest' is 'MAJESTY'.
'for' acts as a link.
(Other definitions for majesty that I've seen before include "Monarch" , "Regal dignity" , "Supreme power" , "title" , "Splendour" .)