The article is devoted to the problem of language interaction in Polish and East Slavic languages phraseology. Polish had a signifi cant impact on the formation of the phraseology of the East Slavic languages of the late XVI – early XIX century, which led to the emergence of similar Polish-Ukrainian-Belarusian-Russian phraseological units. It is often very difficult to determine the donor language. In some cases, the idiom (or proverb) could migrate from one language to another, enriching itself with new elements (in terms of vocabulary or semantics) and returning to the donor language in a new capacity. In the search for the source of phraseology in the article the authors propose to consider the date of the earliest fixation of the unit, the extended context of its use, which may contain linguistic or ethnographic details that help to identify the donor language. The article investigates the origin of one of the most obscure and recalcitrant items in Slavic phraseology: Polish zbić z pantałyku, Belorussian збіць з панталыку, Ukrainian збити з пантелику and Russian сбить с панталыку. In all four languages the meaning is ‘to confuse, befuddle, baffle’. This phraseological expression is shown to be first attested in Ukrainian at the end of the 18th cent.; from Ukrainian it was borrowed into Russian and then migrated into Polish. It is proposed that the expression originated in Ukrainian vernacular on the basis of Polish loanword pontalik ‘ornament, jewel’ adopted in Ukrainian as пантелик.