geyser UK /ˈɡiː.zə/US /ˈɡaɪ.zɚ/noun 4verb 1forms 3 noun4 •A boiling natural spring which throws forth jets of water, mud, etc., at frequent intervals, driven upwards by the expansive power of steam. •A momentary vertical jet or fountain of fluid driven upwards by a violent force. •(South-Africa) A domestic water boiler. •(UK, no longer used) An instantaneous, and often dangerous, hot water heater.Where a Geyser or hot-water heater is used it is a good and wise precaution to see that the bath-room, &c., when it is used is well ventilated. — 1902 verb1 •To (cause to) rush or burst upward like water from a geyser.Four jets of water geysered upward from the sea. Short and wide. He noted it. Ranging salvo. His division was discovered. — 1944 formsgeysered · geysering · geysers