from princeton's wordnet:
1. (noun) nausea, sickness
the state that precedes vomiting
2. (noun) nausea
disgust so strong it makes you feel sick
from webster:
1. (noun) nausea
seasickness; hence, any similar sickness of the stomach accompanied with a propensity to vomit; qualm; squeamishness of the stomach; loathing
from the u.s. national library of medicine:
1. nausea
an unpleasant sensation in the stomach usually accompanied by the urge to vomit. common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses.