A term coined by renowned lexicographer, Professor Thistlewaite, to describe a word that sounds like it should mean something, but in fact means nothing at all.
Example: 'Flibber-Flabber' sounds like a word that would be used to describe a type of exotic cheese, but it is, in fact, the sound of one's shoes flapping wildly in the wind.
C prophets, we have a Lexicon Entry #11: The Snizzle-Frazz for more information on this fascinating topic.