uk â /vÉlËkeÉª.nÉÊ/ us â /vÉËlËkeÉª.noÊ/ plural volcanoes or volcanos. B2 a mountain with a large, circular hole at the top through which lava (= hot liquid rock) gases, steam, and dust are or have been forced out: an extinct/dormant volcano. an active volcano. Erupting volcanoes discharge massive quantities of dust into the stratosphere.