Heretic eruditely holding up speaker (7)
I believe the answer is:
reciter
'speaker' is the definition.
(I know that reciter is a type of speaker)
'heretic eruditely holding up' is the wordplay.
'holding' indicates the answer is hidden within the clue.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'reticer' can be found hidden inside 'heretic eruditely'.
'reticer' back-to-front is 'RECITER'.
(Other definitions for reciter that I've seen before include "Person declaiming" , "Declaimer (of, eg, poem)" , "Reader of poetry" , "Speaker" , "One declaiming" .)