Part of speech one has to repeat (4)
I believe the answer is:
echo
'to repeat' is the definition.
('echo' can be a synonym of 'repeat')
'part of speech one has' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ECHO' can be found hidden inside 'speech one has'.
(Other definitions for echo that I've seen before include "The distant sound" , "Reflect in Czechoslovakia" , "Ape" , "E; reverberation" , "one catches on the rebound?" .)