Ancient texts are old custom almost rejected (5)
I believe the answer is:
sutra
'ancient texts are old custom almost rejected' is the definition.
I can't tell whether this definition defines the answer.
'are old custom almost rejected' is the wordplay.
'are old' becomes 'art' (historic version of 'art').
'custom' becomes 'use' (use is a kind of custom).
'almost' means to remove the last letter (most of the word but not all of it).
'rejected' is a reversal indicator.
'art'+'use'='artuse'
'artuse' with its final letter taken away is 'artus'.
'artus' back-to-front is 'SUTRA'.
Can you help me to learn more?
(Other definitions for sutra that I've seen before include "Book of aphorisms" , "Buddhist literature" , "Sanskrit aphorisms" , "The Kama ..... is a Sanskrit sex manual" , "Collection of Hindu or Buddhist sayings" .)