As nouns the difference between lava and lapilli
is that
lava is the melted rock ejected by a volcano from its crater or fissured sides while
lapilli is 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.
As a proper noun Lava
is one of the twin children of the Lord Rāma and his wife Sita in the Ramayana.