The Collaborative International Dictionary of English v.0.48:

mayonnaise \ma`yon`naise"\, n. [F.]
   A thick white sauce compounded of raw yolks of eggs beaten up
   with olive oil to the consistency near to that of a gel, and
   seasoned with vinegar, pepper, salt, etc.; -- used in
   dressing salads, fish, etc. Also, a dish dressed with this
   sauce.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mayonnaise
    n 1: egg yolks and oil and vinegar [syn: mayonnaise, mayo]

The Devil's Dictionary (1881-1906):

MAYONNAISE, n.  One of the sauces which serve the French in place of a
state religion.