Properly a flower of a reddish blue or deep purple (hyacinth), and hence a precious stone of that colour (Revelation 21:20). It has been supposed to designate the same stone as the ligure (Hebrews leshem) mentioned in Exodus 28:19 as the first stone of the third row in the high priest's breast-plate. In Revelation 9:17 the word is simply descriptive of colour.

Noah Webster's New International Dictionary of the English Language

(n.) See Hyacinth.