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Webster 1913 Edition

‖

Noun.

pl.

[L.

lapillus

a little stone, dim. of

lapis

stone.]

(Min.)

Volcanic ashes, consisting of small, angular, stony fragments or particles.

lapilli ‎(uncountable)

A sphere shaped droplet of molten lava ejected from a volcanic eruption which falls to earth while still at least partially molten, ranging in size from 2 to 64 millimeters.
- 2007 May 8, Henry Fountain, “It’s Still Dark Out, So Why Are the Birds Singing Away?”, in New York Times:
  They also found rounded granules that are probably accretionary lapilli — volcanic hailstones, formed as material gathers in the air.

lapillī