The same endlessly rich Greek dialect (5)
I believe the answer is:
doric
'greek dialect' is the definition.
(I've seen this in another clue)
'the same endlessly rich' is the wordplay.
'the same' becomes 'do' (abbreviation for ditto).
'endlessly' means to remove the last letter.
'rich' with its final letter taken away is 'ric'.
'do'+'ric'='DORIC'
(Other definitions for doric that I've seen before include "Greek architectural style" , "Of the oldest and simplest form of architecture" , "One classical order in architecture" , "One of the Greek orders of architecture" , "Relating to a classical order of architecture" .)