Fanatic's beginning to expect much after the last letter (6)
I believe the answer is:
zealot
'fanatic's' is the definition.
(I've seen this before)
'beginning to expect much after the last letter' is the wordplay.
'beginning to' indicates taking the first letters.
'much' becomes 'alot' (synonyms).
'after' says to put letters next to each other.
'the last letter' becomes 'z' (last letter of the alphabet).
The initial letter of 'expect' is 'e'.
'e'+'alot'='ealot'
'ealot' after 'z' is 'ZEALOT'.
(Other definitions for zealot that I've seen before include "Fervent enthusiast" , "Person militant about a cause" , "A fanatic, driven person" , "Radical" , "Fanatic or extreme enthusiast" .)