la*va*bo n. (pl. -boes) (in the Roman Catholic Church) a towel or basin used for the ritual washing of the celebrant's hands at the offertory of the Mass. - ritual washing of this type. - DATED a washbasin. - a washing trough in a monastery. mid 18th cent.: from Latin, literally 'I will wash', in Lavabo inter innocentes manus meas 'I will wash my hands among the innocent' (Ps. 26:6), which was recited at the washing of hands in the Roman rite. la*va dome n. a mound of viscous lava that has been extruded from a volcanic vent. la*va flow n. a mass of flowing or solidified lava. la*vage n. [MEDICINE] washing out of a body cavity, such as the colon