What is the origin of rutilant?
It is one thing to see greatly varying descendants of Proto-Indo-European words in its daughter languages, as for instance in the very common (and easy to handle) Proto-Indo-European root bher-, bhor- “to carry, bear, bear children,” which appears as bhar- in Sanskrit, pher- in Greek, fer- in Latin, and ber- in Slavic, Armenian, and Germanic (English bear). It is another thing to see wildly variant forms of a Proto-Indo-European root within one language, but Latin offers a good example from the Proto-Indo-European root reudh-, roudh-, rudh- “red.” (The root variant roudh- becomes raud- in Germanic, rēad in Old English (the ēa is a diphthong from au) and red in English.) Roudh- is also the source of Latin rūfus, a dialect word meaning “red, tawny” and also a proper name “Red” (rufous and Rufus in English). Roudh- also yields Latin rōbus “red (of oxen and other animals),” rōbur “oak, red oak” (the adjective rōbustus “of oak, oaken, strong” becomes robust in English). The root variant rudh- yields Latin ruber “red,” rutilus “glowing red,” with its derivative verb rutilāre “to glow with a bright red or golden color,” whose present participle stem rutilant- becomes English rutilant. Rutilant entered English in the 15th century.