Kalmar "carboxyl" tana nufin ƙungiyar aiki a cikin sinadarai na halitta wanda ya ƙunshi carbon atom, oxygen atom mai haɗaka biyu, da ƙungiyar hydroxyl (-COOH). Ana samun wannan rukuni a cikin mahalli masu mahimmanci masu yawa, ciki har da amino acid, fatty acid, da Organic acid. Kalmar “carboxyl” ta fito ne daga haɗin “carbonyl” (yana nufin iskar oxygen mai ɗaure biyu) da “hydroxyl” (yana nufin ƙungiyar -OH).