From the same as kad in the sense of striking fire from a metal forged; a sparkling gem, probably the ruby -- agate.
see HEBREW kad
H3539. kadkod
כַּדְכֹּד noun [masculine] a precious stone, perhaps ruby (from sparkle ?; Aramaic "" is כַּדְכְּדָנָא); ׳כ Ezekiel 27:16 as article of commerce; כַּדְכֹֿד Isaiah 54:12 figurative in promise to Zion.
כְּדֵי see דַּי.
כדר (√ of following; compare Arabic VII. shoot or rush down (of hawk, star, etc.; also of an attacking force) so Thes Fl in DeJob 15:24 Buhl Di and others; see also modern Arabic annoy, vex, reprimand, SpiroVocab.; oftener be dark, gloomy, turbid, whence > כידור = seething tumult, of battle, compare Köii, 147, § 71, 1).