To a sickening extent (2,7)
I believe the answer is:
ad nauseam
'to a sickening extent' is the definition.
(synonyms)
This is all the clue.
(Other definitions for ad nauseam that I've seen before include "to an excessive extent" , "Much too much" , "Excessively, to a sickening extent" , "To a very tiresome degree" , "to a sickening degree" .)