The article examines the famous statement of the author of “Slovo o Polku Igoreve” (“The Tale of Igor’s Campaign”), which characterizes the creative manner of the Old Russian bard Boyan – “he will spread his thoughts on the tree”. The interpretation of “thought” as another name for mistletoe – a plant that parasitizes trees of different types – is proposed. This name is represented in a number of European languages – English mistle(toe), German Mistel, Swedish mistel and phonetically almost coincides with the Russian word thought. In ancient times mistletoe was a cult plant of the Germans, Gauls, Celts, it was attributed special protective and healing properties, and the tree on which the mistletoe grew was considered sacred. Among the Slavs mistletoe was a symbol of fertility, life and immortality. The mistletoe-covered oak was especially revered. It is suggested that the tree mentioned in the “Slovo” and named a “the thought tree” is an oak tree covered with omela. It is possible that the author of the “Slovo” played the phonetic resemblance of two words that denote different, but somewhat similar concepts – a human thought that encompasses time and space, and an unusual plant that spreads on the tree. This assumption allows us to preserve the threefold comparison of Boyan's work, to translate it into real space – mistletoe, wolf, eagle – and not to resort to the idea of an imaginary “thought tree”.