The language which they speak, and which has spread widely to other areas, is Arabic. �Arabic� is not generally used as an adjective except when referring to the language or in a few traditional phrases such as �gum arabic� and �arabic numerals.� Note that in these few phrases the word is not capitalized. Otherwise it is �Arab customs,� �Arab groups,� �Arab countries,� etc. 

A group of Arab individuals is made of Arabs, not �Arabics� or �Arabians.� The noun �Arabian� by itself normally refers to Arabian horses. The other main use of the word is in referring to the collection of stories known as The Arabian Nights.

ahhh, once I�ve read that Arab and Arabian both could be used to denote the inhabitants of Arabia or the Arabian horse.

hope it helps!

Alex Carr