One of the mysteries of the English language finally explained.
A sea-green or turquoise precious stone, often identified as (a form of) turquoise, or (less commonly) variscite.
Late 16th century; earliest use found in Arthur Golding (d. 1606), translator. From classical Latin callais greenish-blue precious stone, turquoise (Pliny), probably from an unattested Greek form *καλλαίς; compare Hellenistic Greek καλλάϊνος (also καλάϊνος) greenish-blue.
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