The report deals with the idioms which were recorded by the Ural Federal University Toponymic expedition during field research in Arkhangelsk oblast, Vologda oblast and Kostroma oblast in 2008--2013, but are not included in Russian dialect dictionaries: саватейки сколачивать «to idle», демьянова уха “lenten soup made with potatoes and onion”, взбодать рёлку, поймать остродыма “to finish harvesting crops” etc. The semantic and motivational reconstruction of these idioms requires the use of the ethnocultural context (folk beliefs, rituals, foklore texts). The author proposes specific motivational solutions and discusses the possibility of prediction of ethnocultural context factors.