The broken plural of the Arabic word جزيرة (jazīra) for island has come to be the proper name for Algeria, its capital, and the islands in its bay, as there were once several small islands in the Bay of Algiers. Most of these islands are now connected to the shore or have been removed. Al-jazā’ir is itself a truncated form of the city's older name of jazā’ir banī mazghannā, Arabic for "the islands of (the tribe) Ait Mazghanna", which was used by early medieval geographers such as al-Idrisi and Yaqut al-Hamawi.
Proper noun 
الجَزَائِر • (al-jazā’ir) pl