The paper discusses the Russian word селезень ‘drake’, which is problematic from the point of view of etymology. This word can be explained as a lexical contamination connected by a grade metathesis to сизый ‘blue-grey’ and зеленый ‘green’: сизый (in Slavic folklore, this adjective is a constant epithet for a drake) and зеленый (this word indicates the plumage colour of the male bird) = *сизелень > *силезень > селезень (because of силезень ‘spleen’). The paper is based on historical and lexicological material and uses dialectal examples that ensure the reliability of the author’s conclusions.