↑de Vaan, Michiel (2008) Etymological Dictionary of Latin and the Other Italic Languages. Leiden: Brill, p. 219/220. ISBN 978-90-04-16797-1
↑Mallory, J. P. & Adams, Douglas Q. (2006) The Oxford introduction to Proto-Indo-European and the Proto-Indo-European world. Oxford: Oxford University Press, 255. ISBN 978-0-19-928791-8