traho.

Unclear. The -h- would normally correspond to Proto-Indo-European *-ǵʰ- or *-gʰ- (compare veho, from Proto-Italic *weɣō, from Proto-Indo-European *weǵʰ-). A relationship with Proto-Germanic *draganą (“to drag, draw”) is debated, since Latin initial t- and Germanic initial *d- is not a usual correspondence. Some consider it impossible for both to be inherited from a common Proto-Indo-European root (though De Vaan thinks they could be related as loans from some common non-Indo-European source). Others derive both from a Proto-Indo-European or post-PIE root *dʰragʰ-, with Latin showing a controversial dissimilation to *dragʰ- (Weiss treats the liquid after the first stop as an essential condition for this "Limited Latin Grassmann's Law"), followed by devoicing of dr to tr (a more generally accepted sound change). Schrijver argues that the presence of -ā- in the perfect stem and in some related forms such as trāgula is a sure sign of an original laryngeal in the root, and proposes *dʰr(e)Hgʰ- as a possible form. De Vaan reconstructs a non-Indo-European (substrate) root *trHgʰ- or *trā̆gʰ-, borrowed into Italic and Celtic, as a potential source of both Latin trahō and Old Irish tethraig (“ran away, receded”), Welsh traul (“trouble, weakness; cost, expense”) < Proto-Celtic *trāglo-. Other possible cognates include * Proto-Celtic *tregess (“foot”), Gothic 𐌸𐍂𐌰𐌲𐌾𐌰𐌽 (þragjan, “to run”), Proto-Slavic *tragъ, but semantically problematic. * Latin tergus (“back, rear”)/Latin tergum, Ancient Greek τρέχω (trékhō), Proto-Germanic *trekaną (“to push, drag, scratch”), *trudaną (“to tread, to step on”)