This article presents an interdisciplinary analysis of the etymology of "pi-" [pi] words in the Russian language. It challenges conventional Proto-Indo-European root systems, proposing an alternative hypothesis that views the root "pi" [pi] as a marker for movement and the flow of liquids. The study integrates linguistic analysis, archaeological evidence of pre-fire cuisine, and folk etymology to demonstrate how words like "pit’" [pitʲ] (to drink), "pitanie" [pʲɪˈtanʲɪɪ̯ə] (nutrition), and "pishcha" [ˈpʲiɕːə] (food), as well as the loanwords "pizza" [ˈpʲit͡sːə] and "pita" [ˈpʲitə], are semantically linked to the ancient practice of rehydration—the softening of solid food in liquid. The paper also explores the onomatopoeic and figurative connections of the root to physiological processes and to vocabulary traditionally assigned to other roots (e.g., "pisat’" [pʲɪˈsatʲ] - to write), through the metaphor of liquid "flow."