[Olog-hai]

All that “mayonnaise” means is a sauce conceived in Mahón, Spain. Ingredients not specified.

What of the original “ketchup”, a fish sauce with no tomato content whatsoever?

[Ray76]

Ketchup is tomato catsup.

[SoothingDave]

http://dictionary.reference.com/browse/mayonnaise?s=t

The dictionary, common sense, and seemingly some federal regulations disagree with you.

[SoothingDave]

http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=169&showFR=1&subpartNode=21:2.0.1.1.41.2