From qaba'; a goblet (as deep like a cover) -- dregs.
see HEBREW qaba'
H6907. qubbaath
קֻבַּ֫עַת noun feminine cup (perhaps loan-word from Assyrian [‡abu°tu], plural ‡abûâtê, probably cups, goblets; compare Arabic flower-cup, calyx); — construct ק ׳הַתַּרְעֵלָה כּוֺס Isaiah 51:17 compare 51:22 (both figurative, and כּוֺס in both probably explanatory gloss, see Commentaries).