Definition of macropinacoid in US English:

macropinacoid

noun

  • A pinacoid parallel to the vertical and macrodiagonal axes of a crystal.

Origin

Late 19th century; earliest use found in Encyclopaedia Britannica.

Pronunciation

macropinacoid

/ˌmakrə(ʊ)ˈpɪnəˌkɔɪd/