A common misspelling of synesthesia/synaesthesia with a GCUI of 225/8,250, or 2.7%. What is surprising about this misspelling is that it occurs in scholarly works and University courses with unusual frequency.
Several groups have released albums named Synesthesia which are often misspelled in discussion boards and in music reviews. Moreover, there is much excellent visualization software that often finds itself under this misspelling.
The -s- in synesthesia is not silent (sin-is-THEE-zha), so it is interesting that people so often leave it out. The alternate (and acceptable) spelling synaesthesia (or synæsthesia if one is truly pretentious) is even more common than the Americanized version, and has a GCUI of 13,900/8,250, or 168.5%