Historically you will bellow (4)
I believe the answer is:
yell
'bellow' is the definition.
(I've seen this in another clue)
'historically you will' is the wordplay.
I cannot quite see how this works, but
'you' could be 'ye' (historical version of 'you') and 'ye' is found within the answer.
'will' could be 'll' (contracted form, as in 'he'll' - 'he will') and 'll' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for yell that I've seen before include "Clement --, politician" , "Loud cry; rhymes with collapsed" , "Give a sudden loud cry" , "Shetland isle" , "Loud sharp cry" .)