rutilus.

Possibly either: * from a derivative of Proto-Indo-European *h₂réw-ti-s ~ *h₂ru-téy-s, from *h₂rew- (“to shine”) + *-tis, perhaps cognate to Proto-Celtic *ruteinos (“shiny reddish, rust colored”), via either: ** If one follows Sen in supposing an origin from older rutulus with labial dissimilation, one can derive this from *rutis (“redness”) + *-elos (desubstantival suffix); ** Via reconstructing -i- as the original second vowel instead of *-e-; some scholars believe that *-i- did not merge with *-e- during vowel reductions before -l-: *** Schaffner reconstructs Proto-Italic *rutilos and segments this as Proto-Indo-European *h₂ruti-lo-; *** Prósper posits instead Proto-Italic *rutiðos, the -ilus in Latin thus serving as a lambdacized counterpart to Latin -idus. * or dissimilated from Proto-Italic *rutrelos (compare Latin clītellae) also with labial dissimilation, from *rutros, variant of *ruðros (“red”) (whence Latin ruber (“red”)) + *-elos, from Proto-Indo-European *h₁rudʰ-ró-s (“red”), from *h₁rewdʰ- (“red”) + *-rós.