Crossword clue: a solid whose bases or ends are any similar, equal, and parallel plane figures, and whose sides are parallelograms.
1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
optical device having a triangular shape and made of glass or quartz; used to deviate a beam or invert an image