Definition of polyiamond in English:

polyiamond

noun

Geometry
  • A planar shape formed by joining a number of identical equilateral triangles by their edges.

Origin

1960s; earliest use found in Scientific American. From poly- + iamond, by analogy, taking the d- of diamond (by an intentional false etymology) to represent either di- or duo-: compare polyabolo, polyomino, etc.

Pronunciation

polyiamond

/ˌpɒlɪˈʌɪəmənd/