1677, variant of M.E.
bulder (c.1300), from a Scand. source akin to Sw. dial.
bullersten "noisy stone" (large stone in a stream, causing water to roar around it), from
bullra "to roar" +
sten "stone." Or the first element may be from
*buller- "round object," from P.Gmc.
*bul-, from PIE
*bhel- "to inflate, swell" (see
bole).