From BiblePortal Wikipedia

King James Dictionary [1]

HY'ACINTH, n. L. hyacinthus.

1. In botany, a genus of plants, of several species, and a great number of varieties. The oriental hyacinth has a large, purplish, bulbous root, from which spring several narrow erect leaves the flower stalk is upright and succulent, and adorned with many bell-shaped flowers,united in a large pyramidical spike, of different colors in the varieties. 2. In mineralogy, a mineral, a variety of zircon, whose crystals,when distinct, have the form of a four-sided prism, terminated by four rhombic planes,which stand on the lateral edges. Its structure is foliated its luster, strong its fracture, conchoidal. Its prevailing color is a hyacinth red, in which the red is more or less tinged with yellow or brown. It is sometimes transparent, and sometimes only translucent.

Hyacinth is a subspecies of pyramidical zircon.

Webster's Dictionary [2]

(1): ( 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.

(2): ( n.) A plant of the genus Camassia (C. Farseri), called also Eastern camass; wild hyacinth.

(3): ( n.) A red variety of zircon, sometimes used as a gem. See Zircon.

(4): ( n.) A bulbous plant of the genus Hyacinthus, bearing beautiful spikes of fragrant flowers. H. orientalis is a common variety.

Holman Bible Dictionary [3]

 Revelation 9:17  Exodus 28:19 Revelation 9:17 Revelation 21:20  Exodus 28:19 Revelation 21:20

Smith's Bible Dictionary [4]

Hyacinth. Used in the Revised Version for jacinth in  Revelation 9:17. It is simply another English spelling of the same Greek word.

Hastings' Dictionary of the Bible [5]

HYACINTH .   Revelation 9:17 RV [Note: Revised Version.]; AV [Note: Authorized Version.] ‘ jacinth .’ See Jewels and Precious Stones.

Hastings' Dictionary of the New Testament [6]

See Jacinth.

International Standard Bible Encyclopedia [7]

hı̄´a sinth ὑάκινθος huákinthos   Revelation 9:17  Revelation 21:20