prism: [16] The etymological idea underlying the word prism is of its shape, that of a ‘sawn-off’ piece. It comes via medieval Latin prisma from Greek prísma, a derivative of the verb prízein ‘saw’. Its optical application emerged in English at the beginning of the 17th century.
1560s, a type of solid figure, from Late Latin prisma, from Greek prisma (Euclid), literally "something sawed," from prizein "to saw" (see prion). Meaning in optics is first attested 1610s.
