Etymologies heretofore proposed for Grk. ταχύ𝗌 ‘swift’, τάχo𝗌 ‘swiftness’, have met little favor. The notion of ‘swiftness’ is frequently a by-product of ‘tension’: e.g., cf. ON snarr literally ‘tightly twisted’ of a string (: snara ‘turn, twist, wring'), but chiefly ‘swift'; and more especially Lat. contendo frequently ‘hasten', or NE speed, OE spēd, OHG spuot ‘speed, success’, ChSl. spěšiti ‘hasten’, all probably from the root ∗spē(i)- in Grk. σπéω ‘draw’. With this in mind one is tempted to derive Grk. ταχύ𝗌 < ∗th
gh- from the root in Av. θang-‘pull, draw’, θanvan-, θanvar- ‘bow’, ChSl. tęgnąti ‘draw’, etc. According to Osthoff the comparative
σσωv,
ττωv represents ∗
éωv with the gradation to be noted in Skt. bahú- ‘much’ and the comparative bánhīya- ‘very stout’, hence the root must be ∗thangh-/∗thṇgh-. In this case all the Slavic forms in tęg- (ChSl. tęgnąti, etc.) represent the weak grade of the root and Slavic ∗tog- in Russ. tugój ‘tight, solid, stretched (of the bow)', Pol. lęgi ‘hard, solid, strong', etc., represents a Pre-Slavic ∗tang-, The representation of IE th by Grk. ∂ though often denied seems clear in several other cases.