Repeat part of speech officially (4)
I believe the answer is:
echo
'repeat' is the definition.
('echo' can be a synonym of 'repeat')
'part of speech officially' is the wordplay.
'part of' indicates a hidden word.
'ECHO' is hidden in the letters of 'speech officially'.
(Other definitions for echo that I've seen before include "Bounced sound" , "Say again or imitate" , "Reminder" , "Sound following" , "Reflection of sound - Greek nymph" .)