Talk of nothing at speed (5)
I believe the answer is:
orate
'talk' is the definition.
(to orate is to give a speech)
'nothing at speed' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'at' is a charade indicator (letters next to each other).
'speed' becomes 'rate' (the speed at which something happens).
'o'+'rate'='ORATE'
'of' is the link.
(Other definitions for orate that I've seen before include "Give speech" , "Hold forth" , "Deliver a speech" , "Talk pompously" , "Speak formally" .)