E. M. Parker; R. J. Hayward (1985),An Afar-English-French dictionary (with Grammatical Notes in English), University of London,→ISBN, page183
Mohamed Hassan Kamil (2015),L’afar: description grammaticale d’une langue couchitique (Djibouti, Erythrée et Ethiopie)[2], Paris: Université Sorbonne Paris Cité (doctoral thesis)
FromProto-Italic*rougā, fromProto-Indo-European*h₁roug-h₂-(“wrinkle”), related to*h₁rewg-(“to roar, belch”), where the sense development would be "to belch" → "to undulate"[1] → "to be rugged" → "crease, wrinkle".[2] Compareructo(“I belch, bring up noisily”). For the development to“street”, compare alsorupta via(literally“path made by force”).
The connection between 'to belch' and 'caterpillar' may be the way in which a caterpillar moves forward, viz. by slowly pushing itself foward (sic), first with its hind legs, thus raising the central part of its body to a curve, which is lowered again when the front legs move forward. This movement may easily call into mind the lowering and raising of the Adam's apple when people belch, or retching movements of the throat when vomiting.
^De Vaan, Michiel (2008), “ruga”, inEtymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill,→ISBN,pages528-29
“ruga”, inCharlton T. Lewis and Charles Short (1879),A Latin Dictionary, Oxford: Clarendon Press
“ruga”, inCharlton T. Lewis (1891),An Elementary Latin Dictionary, New York: Harper & Brothers
"ruga", in Charles du Fresne du Cange’sGlossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
“ruga”, inHarry Thurston Peck, editor (1898),Harper’s Dictionary of Classical Antiquities, New York: Harper & Brothers
