In modern English, the Latin loanword ad nauseam—originally meaning, literally, to sickness—is an adverb meaning to a disgusting or ridiculous degree. It usually applies to an action being repeated so many times that one gets literally or figuratively sick of it. Be careful not to spell it ad nauseum.
Because ad nauseam has been in English a long time, there’s no need to italicize it in normal use.
The phrase ad nauseam is misspelled almost as often as it’s spelled correctly. For example, these writers use the misspelled form:
As we’ve discussed ad infinitum, ad nauseum, t-shirts are not in short supply anywhere. [Christian Science Monitor]
The victimised tone is not utilised ad nauseum, and if he wasn’t even going to name any names then he may as well not have bothered. [Edinburgh Journal]
These writers spell ad nauseam correctly:
I am hoping Franco and Hathaway do better than the awful “wardrobe malfunction” commercial that ABC has been airing ad nauseam. [Salt Lake Tribune]
At this point, every aspect of today’s Giants-Jets game has been broken down ad nauseam, and our ears are bleeding from the trash talk. [Star-Ledger]
I know there are some who criticise Fairtrade, and I’ve heard all the arguments about protectionism ad nauseam. [Guardian]
Even more amusing is the thought that I am still working on the same classical chestnuts my parents had to hear ad nauseam when I was a kid. [Globe and Mail]