The word croissant is a borrowed word.
Borrowed words or loanwords are words that society adopts from foreign languages and makes them part of their usual vocabulary, there are many words that languages borrow from each other, such as croissant, pizza or café, this happens after continuous and close interaction between different cultures.
The word croissant came from the word "crescent." Thus, because of the shape of the croissant, the word was probably borrowed from crescent. So that's how they named the word. By borrowing it from the word crescent. I hope this answer helped you.