Speak pompously of ordinary degree (5)
I believe the answer is:
orate
'speak pompously' is the definition.
(to orate is to give a speech)
'ordinary degree' is the wordplay.
'ordinary' becomes 'O' (abbreviation e.g. O-Levels).
'degree' becomes 'rate' (I've seen this before).
'o'+'rate'='ORATE'
'of' is the link.
(Other definitions for orate that I've seen before include "Erato (anag.)" , "Pontificate" , "Make a formal address" , "Speak publicly" , "make speeches" .)