upthrow verb 3noun 1forms 4 verb3 •To throw up (a mass of material) from below, causing a fault. •To be thrown up from below, causing a fault. •(literary, no longer used) To throw or cast upwards.For fifty tons of water were upthrown / By them per hour [...]. — 1819 noun1 •A fault in which a mass of material has been thrown up from below. formsupthrew · upthrown · upthrowing · upthrows