Arabian
"Arabian" is the adjective that relates to the Arabian Peninsula. "Arabians" are not an ethnic group; "Arabian" is not a synonym for "Arab".
If "Arabians" were used as a noun referring to people, it would refer to people from the Arabian Peninsula (i.e. Saudi Arabia, Oman, Yemen, Kuwait, the United Arab Emirates, Bahrain, Qatar and Jordan.
If "Arabians" were used as a noun referring to people, it would refer to people from the Arabian Peninsula (i.e. Saudi Arabia, Oman, Yemen, Kuwait, the United Arab Emirates, Bahrain, Qatar and Jordan.
Example:
The three traditional components of the Arab World are the Maghreb (North Africa), the Mashriq (the Levant) and the Arabian Peninsula.
The three traditional components of the Arab World are the Maghreb (North Africa), the Mashriq (the Levant) and the Arabian Peninsula.