From qabab; a hollow, i.e. Vessel used as a (dry) measure -- cab.
see HEBREW qabab
H6894. qab
קַב noun [masculine] kab (Late Hebrew id.; Syriac ; Talmud קַבָא); — a measure of capacity, Biblical Hebrew only dry measure, הַקַּב רֹבַע 2 Kings 6:25 4-Jankab; on size of קַב = 4 לֹג = 1/6 סְאָה = 1/6 הִין = approximately 2 litres see NowArchaeology i. 202 f. BenzArchaeology 182.