Knowing parade must start late (4)
I believe the answer is:
arch
'knowing' is the definition.
(thesaurus)
'parade must start late' is the wordplay.
'parade' becomes 'march' ('march' can be a synonym of 'parade').
'must start late' means to remove the first letter.
'march' with its first letter removed is 'ARCH'.
(Other definitions for arch that I've seen before include "Vaulted opening" , "Cunning; playful" , "Curve of a bridge" , "Curve of the foot" , "Knowing, sly" .)