The article is devoted to the etymology of the Old Russian word puz ‘a dry measure unit’. The word’s meaning is considered from the point of view of its interrelationships with those of Rus. puzo ‘belly’ and its cognates, concluding that puz shows no underlying semantics of ‘a body part’ or ‘swelling’ that would be required to etymologically link it to puzo, but rather bears a close formal and semantic resemblance to Baltic-Finnic lexemes that refer to a ‘coil, roll, bobbin’, or ‘а cylindershaped wooden vessel’. Confinement of the word under study to North-Western Russian dialects is also noted, as well as the fact that a number of other North Russian ‘vessel’ words have been found to be borrowings. The possibility of a Slavic origin for the Baltic-Finnic source and its secondary borrowing into North Russian dialects is also discussed but not accepted. Thus the author puts forward a version of a Baltic-Finnic origin for the word.