Declaim zero cost (5)
I believe the answer is:
orate
'declaim' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for orate that I've seen before include "Speak pompously and at length" , "Make a formal speech" , "Harangue" , "Speak publicly" , "Make a formal address" .)