From Moby Thesaurus II by Grady Ward, 1.0 :
25 Moby Thesaurus words for "one and only":
I, absolute, ace, alone, atom, azygous, celibate, first and last,
impair, lone, monad, no other, none else, nothing else,
nought beside, odd, one, only, only-begotten, singular, sole,
unique, unit, unpaired, unrepeated