noun pl. volcanoes -·noes or volcanos -·nos

1. a vent in the earth's crust through which molten rock (lava), rock fragments, gases, ashes, etc. are ejected from the earth's interior: a volcano is active while erupting, dormant during a long period of inactivity, or extinct when all activity has finally ceased
2. a cone-shaped hill or mountain, wholly or chiefly of volcanic materials, built up around the vent, usually so as to form a crater

Etymology: It < L Volcanus, Vulcan