Zero speed so to speak (5)
I believe the answer is:
orate
'to speak' is the definition.
(orating is a kind of speaking)
'zero speed' is the wordplay.
'zero' becomes 'O' (O resembles 0).
'speed' becomes 'rate' (the speed at which something happens).
'o'+'rate'='ORATE'
'so' acts as a link.
(Other definitions for orate that I've seen before include "Make a formal speech" , "Make a flowery speech" , "Speak formally" , "Speechify" , "Declaim or rant" .)