Letter from Eliot answered (4)
I believe the answer is:
iota
'letter' is the definition.
(iota is a kind of letter)
'from eliot answered' is the wordplay.
'from' says the answer is hidden in the clue.
'IOTA' is hidden within 'eliot answered'.
(Other definitions for iota that I've seen before include "Just a jot, like Greek letter" , "Jot, particle" , "European letter" , "Ninthe letter of the Greek alphabet" , "Jot or tittle" .)