Learn Italian: Quel proprietario è disonesto e non ha restituito i soldi. - That owner is dishonest and he did not return the money.

It uses the negative prefix dis- attached to the base adjective onesto (honest). Just like in English, adding dis- reverses the meaning to create the exact opposite. You will also see this in Italian words like disoccupato (unemployed) or disordinato (messy).

Why do we use Quel instead of Quello before proprietario?

The demonstrative adjective quello changes its ending to match the definite article the noun would normally take. Because we say il proprietario, quello matches the il pattern and becomes quel. You would only use quello before a noun that takes lo, like quello specchio.

Why use restituito instead of ritornato to say that he didn't return the money?

In Italian, the verb you choose depends on what kind of returning you are doing. Restituire specifically means "to give back" an item, like money or a borrowed book. You use ritornare when talking about a person or animal returning to a location.

Why is i soldi plural when the English translation says "the money"?