A letter from an amusing person (9)
I believe the answer is:
character
This could be a double definition.
'a letter' is the first definition.
(written character)
'an amusing person' is the second definition.
'character' can be an answer for 'person' (character is a kind of person). I am unsure of the 'an amusing' bit.
'from' acts as a link.
Can you help me to learn more?
(Other definitions for character that I've seen before include "Person in a play; letter" , "Letter or number" , "Part" , "Personal moral qualities" , "Letter or figure" .)