Correct spelling, explanation: the word Brazilian was created in a very common way: by adding the -ian suffix (from, related to, or like) to the basic word (Brazil). That means its construction is simple. Just look at the other examples: Arabian, Bulgarian, and Catalonian. There’s no need to put any other element in it. Brazilian is the only correct form and Brazillian is incorrect.

Incorrect spelling, explanation: many derived words in English have double consonants. However, this is not the case with the verb/noun Brazilian. It consists of two parts: the word-formation base and the suffix. The base is Brazil and the suffix is -ian. We shouldn’t double the -l letter, we have no reason to do so. Brazillian is incorrect.

Definition of Brazilian:
1. adjective, relating to Brazil or its inhabitants
I am proud of my Brazilian roots.
The Brazilian attack put France’s defenders under pressure.
2. noun, a native or inhabitant of Brazil
When I was on vacation, I met a lot of Brazilians.
While I was waiting for the bus, a Brazilian approached me and asked for directions.

Collocations with Brazilian:
Some most commonly used collocations include: Brazilian accent and Brazilian team.
Nina spoke Portuguese with a Brazilian accent.
The Brazilian team is regarded as unbeatable.

Incorrect spelling

Incorrect spelling