“Nullification” all the way. It’s not so beautiful, but it’s so dreadful sounding, it’s almost beautiful, if in a twisted kind of way. Another word in this category is “annhialation.”
The least beautiful word? “Peacock!” We might as well call it the Urinegenitals bird! Beautiful bird, terrible name.
“Cellar Door” is supposed to be the most beautiful word, based on the way it sounds; not the meaning of the word. en.wikipedia.org/wiki/Cellar_door
(Donnie Darko was a great movie, if you haven’t seen it I suggest you rent it.)
I would say that the most beautiful word is ‘free’. Whether you mean ‘Free beer’ or ‘Free speech’ I love it when things are free.
sator arepo tenet opera rotas (which also is an anagram for “paternoster ao ao,” meaning “our father” in latin, and the a’s and o’s standing for “alpha and omega” twice)