Rapid sand filtration is a purely physical drinking water purification method. Rapid sand filters (RSF) provide rapid and efficient removal of relatively large suspended particles. Two types of RSF are typically used: rapid gravity and rapid pressure sand filters. For the provision of safe drinking water, RSFs require adequate pre-treatment (usually coagulation-flocculation) and post-treatment (usually disinfection with chlorine).
with great suddenness the car in front stopped abruptly, and we almost hit it Synonyms short, suddenlyRelated Words surprisingly, unexpectedly; directly, immediately, incontinently, instantaneously, instantly, promptly, pronto, right, right away, right off, straightaway; fast, full-tilt, posthaste, quick, quickly, rapidly, readily, snappily, ...
SYNONYMY NOTE: steep 1 suggests such sharpness of rise or slope as to make ascent or descent very difficult [a steep hill]; abrupt implies a sharper degree of inclination in a surface breaking off suddenly from the level [an abrupt bank at the river's edge]; precipitous suggests the abrupt and headlong drop of a precipice [a precipitous height]; sheer 1 applies to that which is perpendicular, or almost so, and unbroken throughout its length [cliffs falling sheer to the sea]