Толковый словарь английского языка Oxford English Reference - quid pro quo

n. 1 a thing given as compensation. 2 return made (for a gift, favour, etc.). Etymology: L, = something for something QUID 1. n. (pl. same) Brit. sl. one pound sterling. Phrases and idioms not the full quid Austral. sl. mentally deficient. quids in sl. in a position of profit. Etymology: prob. f. quid the nature of a thing f. L quid what, something 2. n. a lump of tobacco for chewing. Etymology: dial. var. of CUD