Is the word oitavo the same in Brazilian and European Portuguese?

Yes

The word "oitavo" is identical in meaning, spelling, and grammar in both Brazilian and Continental Portuguese. The only difference is in pronunciation. In Brazilian Portuguese, the vowels are generally more "open" and the syllables are articulated more clearly and rhythmically. In Continental Portuguese, the unstressed vowels are more "closed" or reduced, which often makes the word sound more compressed or "consonantal."

Brazilian Portuguese Examples

1. Ele mora no oitavo andar. (He lives on the eighth floor.)
2. Eu cheguei em oitavo lugar na competição. (I finished in eighth place in the competition.)
3. Meu filho está no oitavo ano. (My son is in eighth grade.)
4. Ela foi a oitava pessoa a chegar na festa. (She was the eighth person to arrive at the party.)
5. O oitavo capítulo do livro é o meu favorito. (The eighth chapter of the book is my favorite.)

Portuguese (Portugal) Examples

1. Ele mora no oitavo andar. (He lives on the eighth floor.)
2. Fiquei em oitavo na competição. (I came in eighth in the competition.)
3. O meu filho está no oitavo ano. (My son is in eighth grade.)
4. Ela foi a oitava pessoa a chegar à festa. (She was the eighth person to arrive at the party.)
5. O oitavo capítulo do livro é o meu preferido. (The eighth chapter of the book is my favorite.)