Assorted others have right to be more terse (7)
I believe the answer is:
shorter
'more terse' is the definition.
('short' can be a synonym of 'terse')
'assorted others have right' is the wordplay.
'assorted' indicates an anagram.
'have' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'others' with letters rearranged gives 'shoter'.
'shoter' placed around 'r' is 'SHORTER'.
'to be' acts as a link.
(Other definitions for shorter that I've seen before include "Brusquer" , "Not so tall" , "With less length" , "More limited in duration" , "More lacking in length" .)