It is commonly called alumina, and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It commonly occurs in its crystalline polymorphic phase Î±-Al 2 O 3, in which it composes the mineral corundum, varieties of which form the precious gemstones ruby and sapphire.
rain cloud. (meteorology). Any cloud from which rain falls; a popular term having no technical denotation. 1  Facebook. 2  Twitter.
âº a tall, spinning column of air that moves across the surface of the land or sea. Thesaurus: synonyms and related words. Precipitation: stormy weather. blow. blow up. bolt. cyclone. funnel cloud.