Talk hosted by professor, a teacher (5)
I believe the answer is:
orate
'talk' is the definition.
(orating is a kind of talking)
'hosted by professor a teacher' is the wordplay.
'hosted by' indicates the answer is hidden within the clue (the answer is hosted or welcomed by the clue).
'ORATE' can be found hidden inside 'professor a teacher'.
(Other definitions for orate that I've seen before include "Deliver a speech" , "Speak in public" , "Speak publicly" , "Harangue" , "Speak like Cicero?" .)