lava

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Molten rock that reaches the earth's surface through a volcano or fissure.
2. n. The rock formed by the cooling and solidifying of molten rock.

Century Dictionary and Cyclopedia

1. n. Molten rock which issues from a volcano during an eruption; the same when cooled and hardened. Lavas after hardening differ much in structure and texture. Some are entirely made up of an interlaced mass of crystals, others are entirely vitreous, as in the case of obsidian or volcanic glass. Others, again, have a partially glassy matrix, in which crystals are embedded—this last being the most common arrangement. Lavas also vary much in respect to compactness; some have an open cellular structure, while others are very compact. The specific gravity of lava varies in the different kinds from 2.37 to 3.22. The heavier or more basic kinds contain much magnetite or titaniferous iron, together with augite and olivin. These contain from 45 to 50 per cent, of silica, and to this class belong the basalts, dolerites, and nepheline and leucite lavas. The lighter or more acid varieties of lava contain from 60 to 80 per cent, or more of silica. In this class are included the trachytes and rhyolites, as well as most of the pitchstones, obsidians, and pumice. There are also varieties intermediate between the acid and the basic, such as augite andesite and hornblende andesite. Many volcanoes—at least during certain stages of their existence—throw out fragmentary materials only, and these are sometimes ejected during the same period of activity in which molten lava is poured forth. Among these fragmentary materials ashes, sand, lapilli, and even large angular masses occur. Portions of the molten material within the pipe of the crater are sometimes hurled aloft, and fall in the form of bombs, or in rough irregular masses, like furnace-slag. Some volcanoes consist entirely of these fragmentary materials; others are chiefly made up of lava which became consolidated after ejection; in many cases, however, the mass of the cone has been built up by alternations of fragmentary and fluid material, and the whole is frequently bound together by dikes and sheets of lava forced into cracks formed during the operation.

Wiktionary

1. n. The melted rock ejected by a volcano from its crater or fissured sides.
2. n. magma
3. n. lava

GNU Webster's 1913

1. n. The melted rock ejected by a volcano from its top or fissured sides. It flows out in streams sometimes miles in length. It also issues from fissures in the earth's surface, and forms beds covering many square miles, as in the Northwestern United States.

WordNet 3.0

1. n. rock that in its molten form (as magma) issues from volcanos; lava is what magma is called when it reaches the surface