Arab, Arabian, Arabic
1. These three terms refer to different aspects of Arabia and its people: Arab means a member of the Semitic people now inhabiting large parts of the Middle East and North Africa, and is also used as a quasi-adjective before a noun (the Arab people / Arab hopes / Arab philosophy); Arabian is an adjective having geographical reference to Arabia (the Arabian peninsula / an Arabian camel / Arabian fauna); and Arabic is a noun and adjective denoting a language (Do you speak Arabic? / Arabic literature).
2. Arabic is written with a capital initial in the expression Arabic numerals (the numbers 1, 2, 3, etc., as distinct from the Roman numerals I, II, III, etc.). It is written with a small initial in gum arabic, a type of gum exuded by African acacia trees.
3. The expression street Arab, first recorded in 1859, and for about a century commonly applied to a homeless child or other vagrant living on the streets, is now regarded as offensive and is rarely used.

Modern English usage. 2014.