Memory - and the end of past prestige (6)
I believe the answer is:
cachet
'prestige' is the definition.
(synonyms)
'memory and the end of past' is the wordplay.
'memory' becomes 'cache' (I've seen this before).
'and' says to put letters next to each other.
'the end of' suggests the final letters.
The final letter of 'past' is 't'.
'cache'+'t'='CACHET'
(Other definitions for cachet that I've seen before include "Seal; mark of prestige" , "Distinguishing mark or seal" , "Prestige - seal of approval" , "Mark of approval" , "(Mark of) distinction" .)