Lewis & Short

1. ĭon, ĭi, n. [ἴον].

  1. I. A kind of violet, Plin. 21, 11, 38, § 64; plur.: ia, id. 21, 6, 14, § 27.
  2. II. A precious stone of a violet color, Plin. 37, 10, 61, § 170.