Endless, awful sameness, as a whole (2,5)
I believe the answer is:
en masse
'as a whole' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
(Other definitions for en masse that I've seen before include "as a bunch" , "In force" , "All together (Fr.)" , "As a body (Fr.)" , "Sees man (anag.)" .)