In Latin, to a sickening extent (2,7)

I believe the answer is:

ad nauseam

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'to a sickening extent' is the definition.
(synonyms)

I don't understand how the rest of the clue works.

(Other definitions for ad nauseam that I've seen before include "seasickness pills like this would be counterproductive?" , "On and on - would make you sick" , "to an excessive extent" , "Past the stage of enjoying" , "To a very tiresome degree" .)

I've seen this clue in The Daily Express.

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