Reconstruction:Proto-Slavic/sadlo

• Ultimately from *sad- +‎ *-lo. For the formation compare:
  • *dagljь, *jьzgaga, *žeťi
  • *prǫglo, *prǫga, *pręťi
  • *vǫzlъ, *vǫza, *vęzati

(it's not derived from *saditi, in this case form *sadilo/*sadьlo is expected, it's unclear why i/ь would be dropped; and not directly from *sěsti > *sědlo)

• Alternatively from metathesis of earlier *sāldom (cf. *modliti). Cognate with Old Prussian saltan n, Old Irish saill, sall, saillim

*sadlo n

1. fat

• *saditi (“to plant”)

• Vasmer (Fasmer), Max (Maks) (1964–1973), “сало”, in Etimologičeskij slovarʹ russkovo jazyka [Etymological Dictionary of the Russian Language] (in Russian), translated from German and supplemented by Trubačóv Oleg, Moscow: Progress
• Černyx, P. Ja. (1999), “сало”, in Istoriko-etimologičeskij slovarʹ russkovo jazyka [Historical-Etymological Dictionary of the Russian Language] (in Russian), volume 2, 3rd reprint edition, Moscow: Russkij jazyk, page 136
• Šanskij, N. M. (2004), “сало”, in Školʹnyj etimologičeskij slovarʹ russkovo jazyka [School Etymological Dictionary of the Russian Language] (in Russian), Moscow: Drofa
• Martynov V. V. (1982), “Прусско-славянские эксклюзивные изолексы”, in Этимология, Moscow: Nauka, page 9
• Martynov V. V. (1985), “Глоттогенез славян”, in Вопросы языкознания, volume 6, Moscow: Nauka, page 49