|Noah Webster's Dictionary|
1. (n.) A bulbous plant of the genus Hyacinthus, bearing beautiful spikes of fragrant flowers. H. orientalis is a common variety.
2. (n.) A plant of the genus Camassia (C. Farseri), called also Eastern camass; wild hyacinth.
3. (n.) The name also given to Scilla Peruviana, a Mediterranean plant, one variety of which produces white, and another blue, flowers; -- called also, from a mistake as to its origin, Hyacinth of Peru.
4. (n.) A red variety of zircon, sometimes used as a gem. See Zircon.
Int. Standard Bible Encyclopedia
hi'-a-sinth (huakinthos): the Revised Version (British and American) uses this word in Revelation 9:17 for the King James Version "jacinth," with reference, not to stone, but to dark-purple color. In Revelation 21:20, where stone is meant, the Revised Version (British and American) translations "sapphire."
Hyacinth (1 Occurrence)
Revelation 9:17 Thus I saw the horses in the vision, and those who sat on them, having breastplates of fiery red, hyacinth blue, and sulfur yellow; and the heads of lions. Out of their mouths proceed fire, smoke, and sulfur. (WEB ASV NAS)