Summary established after excavation (6)
I believe the answer is:
digest
'summary' is the definition.
(thesaurus)
'established after excavation' is the wordplay.
'established' becomes 'est' (I've seen this in other clues).
'after' says to put letters next to each other.
'excavation' becomes 'dig' ('dig' can be a synonym of 'excavation'**).
'est' after 'dig' is 'DIGEST'.
(Other definitions for digest that I've seen before include "Collection of shortened versions" , "Absorb, in stomach or mind" , "Take in (information or food)" , "Think over, absorb into the mind" , "Long walk, itinerant person" .)