This is the 506th most frequent French word.
roi
King
In this sentence, 'roi' is used as a noun meaning 'king', referring to a royal ruler.
Le roi vit dans un grand palais.
The king lives in a large palace.
Here, 'roi' is used metaphorically to suggest someone is treated with exceptional care and respect, like a king would be.
Il est traité comme un roi par ses amis.
He is treated like a king by his friends.
In this instance, 'roi' is part of a proper noun (a restaurant name) and refers to something named in honor of a king.