nausea, noun; nauseate, verb; nauseous, nauseated, and nauseating, adjectives.
Note: Purists insist that nauseous means “causing nausea,” as in the nauseous roller-coaster ride, and that nauseated means “feeling nausea,” as in the nauseated student rushed from the room. But these days, both adjectives have both meanings. In formal writing, however, it’s best to observe the distinctions. Consider the following:
The problem is whether nauseous can be restricted to meaning “causing nausea” and nauseated to meaning “feeling nausea,” which orderly division is what most Edited English tries to enforce. But alas for neatness, both adjectives have both meanings, though a few dictionaries insist that nauseous, meaning “feeling nausea,” is limited to Colloquial use. Best advice: follow the Edited English practice in speech and writing, and no one will object. In adjunct use nauseous and nauseating, meaning “causing nausea,” are roughly interchangeable in both adjunct and predicate adjective use and get a great deal of Standard figurative use meaning “sickening, disgusting.”
—Kenneth G. Wilson The Columbia Guide to Standard American English (1993)