At the bitter end, throes can be briefer (7)
I believe the answer is:
shorter
'briefer' is the definition.
('short' can be a synonym of 'brief')
'at the bitter end throes can be' is the wordplay.
'at' says to put letters next to each other.
'end' says to take the final letters.
'can be' is an anagram indicator.
The final letter of 'bitter' is 'r'.
'throes' anagrammed gives 'shorte'.
'r' put after 'shorte' is 'SHORTER'.
(Other definitions for shorter that I've seen before include "Lower in stature" , "More limited in duration" , "Brusquer" , "More lacking in length" , "Not so tall" .)