Definition of focaloid in English:

focaloid

noun

Mathematics
  • A shell bounded by two confocal ellipsoidal surfaces, especially (in early use) one that is infinitely thin.

Origin

Late 19th century; earliest use found in William Thomson (1819–1890), archbishop of York. From focal + -oid.

Pronunciation

focaloid

/ˈfəʊkəlɔɪd/