unique
The Italian word 'unico' is used to describe something as being one of a kind or unique. It can be used as an adjective to describe a noun, such as 'un libro unico' (a unique book), or as an adverb to modify a verb, such as 'lavorare in modo unico' (to work in a unique way).
You are the only one who really understands.
In this context, 'unico' is used to portray someone as being special or singular, meaning that no one besides them has the capacity to truly understand.
This is the only book I'm missing.
Here, 'unico' is used to indicate the sole instance or item of something, meaning that among all potentially missing items, this book is the single one that is absent from the speaker's possession.
Luca is one of a kind.
In this sentence, 'unico' is used as part of the Italian phrase meaning 'one of a kind', used to describe someone or something as being unique or unparalleled in their respective domain or category.