From rabah; multiplication, i.e. Percentage or bonus in addition to principal -- increase, unjust gain.
see HEBREW rabah
H8636. tarbith
תַרְבִּית noun feminine increment, interest, usury (= מַרְבִּית
1b; compare (on both) Arabic IV. take usury, interest, usury, Syriac ; SaalschützMos. Recht (ii. 1848), 859 HoelemannLetzte Bibelstud. (1885), 297 f. DiLeviticus 25:36 BennHast. DB DEBT); — always absolute ׳ת: + נֶשֶׁךְ 25:36 (H), Ezekiel 18:17; 22:12; Proverbs 28:8; "" id. Ezekiel 18:8, 13.