* Arabian refers to a person from the Arabian Peninsula. This peninsula is a geographical region in Southwest Asia, encompassing countries like Saudi Arabia, Yemen, Oman, the United Arab Emirates, Qatar, Bahrain, and Kuwait.
* Arabic refers to a language spoken by Arabs. It is the official language of many countries in the Middle East and North Africa, including those mentioned above.
Therefore, while someone from the Arabian Peninsula is likely to speak Arabic, not everyone who speaks Arabic is from the Arabian Peninsula. For example, many people in Egypt, Lebanon, Syria, and other countries outside of the Arabian Peninsula speak Arabic as their native language.
Nationality refers to the country of citizenship. So, someone from Saudi Arabia would have Saudi nationality, while someone from Yemen would have Yemeni nationality, and so on.