Summons comedian to entertain Reading, perhaps (4)
I believe the answer is:
writ
'summons' is the definition.
(legal summons)
'comedian to entertain reading perhaps' is the wordplay.
'comedian' becomes 'wit' (a witty person).
'to entertain' is an insertion indicator.
'reading perhaps' becomes 'R' (one of the traditional three R's of education).
'wit' placed around 'r' is 'WRIT'.
(Other definitions for writ that I've seen before include "Court order document" , "What scribe did" , "Legal document (usually issued)" , "It may be served" , "Sealed document" .)