Definify.com
Webster 1913 Edition
Rupert's drop
Ru′pert’s dropˊ
.A kind of glass drop with a long tail, made by dropping melted glass into water. It is remarkable for bursting into fragments when the surface is scratched or the tail broken; – so called from Prince
Rupert
, nephew of Charles I., by whom they were first brought to England. Called also Rupert’s ball
, and glass tear
.