nuts, the word unique is very interesting
because it is the canonical example of an absolute
grammatical term. It is unable to be modified by any adverb or used in a quantitative comparison
. Either a thing can be described as unique or it cannot. A thing cannot be very
ly unique, more unique than a breadbox
, less unique than a ham sandwich
-- or anything other than unique
. Or as Midori suggests: perhaps everything
Dictionary.com tells it like this: " . . . unique is the paradigmatic absolute term, a shibboleth that distinguishes between those who understand that such a term cannot be modified by an adverb of degree or a comparative adverb and those who do not."
Other so-called absolute terms are absolute, chief, complete, perfect, prime, equal, and parallel -- although in non-mathematical usage the last three have a little wiggle room.