^ Beekes, Robert S. P. (2010) “τρέω”, in Etymological Dictionary of Greek (Leiden Indo-European Etymological Dictionary Series; 10), volume II, with the assistance of Lucien van Beek, Leiden, Boston: Brill, →ISBN, pages 1507-1508
^ Cheung, Johnny (2007) “*θrah-”, in Etymological Dictionary of the Iranian Verb (Leiden Indo-European Etymological Dictionary Series; 2), Leiden, Boston: Brill, →ISBN, pages 393-394
↑ 5.05.1De Vaan, Michiel (2008) “terreō”, in Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill, →ISBN, page 617