The thinking is that unique properly only describes what is unequaled or otherwise distinct from all others. Just as something cannot be more "only" than another, it cannot be more unique than another.

UNIQUE definition: existing as the only one or as the sole example; single; solitary in type or characteristics. See examples of unique used in a sentence.

if something is unique to a place or situation, it only exists in that place or situation:

very special or unusual. The preview offers a unique opportunity to see the show without the crowds. This house has many unique features, including a 45-foot-long outdoor swimming pool. He …

You can use unique to describe things that you admire because they are very unusual and special.

unique 1. used to mean 'the only one' If something is unique, it is the only thing of its kind. This is a unique opportunity. Humans are unique because they have the capacity to choose what they do.

Unique is normally taken to describe an absolute state, i.e. one that cannot be qualified. Thus something is either unique or not unique; it cannot be rather unique or very unique.

Unique definition: Being the only one of its kind.

Unique refers to something that is one of a kind, distinct or unlike anything else. It may refer to an individual, an object, an idea, a situation or a circumstance that stands out from others due to …

6 days ago · unique (comparative uniquer or more unique, superlative uniquest or most unique) (not comparable) Being the only one of its kind; unequaled, unparalleled or unmatched.