From an unused root meaning properly, to dig through; a pot or furnace (as if excavated) -- furnace. Compare kiyr.
see HEBREW kiyr
H3564. kuwr
כּוּר noun [masculine] smelting-pot or furnace (Arabic ; Late Hebrew id.; Aramaic id., ; Ethiopic ) — pot or furnace for smelting metals, but always in metaphor or simile of human sufferings in punishment or discipline: iron (figurative of Egypt as place of bondage) ׳מִכּ הַבַּרְזֶל Deuteronomy 4:20; Jeremiah 11:4, כ ׳מִתּוֺךְ ׳הַבּ 1 Kings 8:51; gold ׳כ לַזָּהָב Proverbs 17:3 = 27:21 ("" מַצְרֵף); various metals Ezekiel 22:18, 20, 22; once עֹ֑נִי בְּכוּר Isaiah 48:10 in a smelting-pot of affliction.