Perhaps from chalam (and thus dream-stone); a gem, probably the amethyst -- amethyst.
see HEBREW chalam
H306. achlamah
אַחְלָ֑מָה noun feminine perhaps amethyst (etymology dubious; below חלם Thes q. v.; HalJAs 7, x. 426 from חלם être fort, solide; Di Kn compare Talmud חַלְמִית, malva & think of green malachite; DlHA 36 N derived from Aramaic land A—lamû), amethyst according to ᵑ9 ᵐ5 Josephus; see also LagGGA 1884, 285, but compare Di; one of the gems on the ephod Exodus 28:19; 39:12.