Power of speech (5)
I believe the answer is:
voice
I believe this is a double definition.
'power' is the first definition.
(I have seen 'Power of speaking ' mean 'voice' so perhaps 'power' could also mean 'voice')
'speech' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for voice that I've seen before include "Power of speech" , "Wallop" , "Opinion; express in words" , "Utter - part" , "Articulate" .)