Learned head missing -- say again (7)
I believe the answer is:
iterate
'say again' is the definition.
(to iterate is say something again)
'learned head missing' is the wordplay.
'learned' becomes 'literate' (synonyms).
'head missing' means to remove the first letter.
'literate' with its initial letter taken off is 'ITERATE'.
(Other definitions for iterate that I've seen before include "Recapitulate" , "Say again, repeat" , "Repeat, state again" , "Utter or perform repeatedly" , "State repeatedly, say again" .)