In his wwftd the other day, tsuwm noted what he referred to as a bit of fanciful etymology:
sneeze is apparently an alteration of fnese
due to misreading or misprinting it with the
old-style s (which looked like an elongated f)
after the initial combination fn- had become
unfamiliar.

Not quite what AHD3 has to say about it. Apparently the f fell off the word for what would seem to me to be obvious reasons and the s got tacked on in its place some time later by analogy with words like snort and snore. A transitional form nese is reported.

http://www.bartleby.com/61/96/S0509600.html


AHD3 is a little more explicit than this from AHD4, but you have to go to the brick and mortar dictionary for that.