The Collaborative International Dictionary of English v.0.48:

Nausea \Nau"se*a\ (? or ?), n. [L., fr. Gr. ?, fr. nay^s ship.
   See Nave of a church, and cf. Noise.]
   Seasickness; hence, any similar sickness of the stomach
   accompanied with a propensity to vomit; qualm; squeamishness
   of the stomach; loathing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nausea
    n 1: the state that precedes vomiting [syn: nausea,
         sickness]
    2: disgust so strong it makes you feel sick