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.
Noun. 1. rain-water falling in drops from vapor condensed in the atmosphere. rainfall. monsoon-any wind that changes direction with the seasons. downfall, precipitation-the falling to earth of any form of water (rain or snow or hail or sleet or mist). raindrop-a drop of rain.