Outstanding English excavation supported by National Trust (7)
I believe the answer is:
eminent
'outstanding' is the definition.
(thesaurus)
'english excavation supported by national trust' is the wordplay.
'english' becomes 'e' (abbreviation).
'excavation' becomes 'mine' (mine is a kind of excavation).
'supported by' is a charade indicator (letters next to each other) (letters go below - in down clue).
'national trust' becomes 'nt'.
'e'+'mine'+'nt'='EMINENT'
(Other definitions for eminent that I've seen before include "Noted" , "Outstanding or distinguished (7)" , "High" , "Notable, outstanding" , "Respected; notable" .)