Largely expected firmament of Twilight? (5)
I believe the answer is:
dusky
'twilight?' is the definition.
(I know that dusky can be written as dusky)
'largely expected firmament' is the wordplay.
'largely' means to remove the last letter.
'expected' becomes 'due' (similar in meaning).
'firmament' becomes 'sky' (sky is a kind of firmament).
'due' with its last letter taken away is 'du'.
'du'+'sky'='DUSKY'
'of' acts as a link.
(Other definitions for dusky that I've seen before include "Shadowy or dark-coloured" , "Shadowy, darkish" , "Dark-complexioned" , "Dark shaded" , "Swarthy" .)