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Cette œuvre est unique dans le monde.
This work is unique in the world.
Being the only one of its kind; unlike anything else.
Il possède un talent unique.
He possesses a unique talent.
Used to emphasize rarity or singularity.
Being the only one; sole.
C'est la seule et unique solution.
It is the one and only solution.
Often used with 'seul' for emphasis (le seul et unique).
Do not use 'unique' to mean 'weird' in French. If you say 'Il est unique', you mean he is special/one-of-a-kind, not that he is strange.
From Latin 'unicus', meaning 'single' or 'only'.
In French, 'unique' strictly means 'one of a kind' or 'sole'. It does not carry the informal English connotation of 'weird' or 'strange'. To express 'weird', use 'bizarre' or 'étrange'.