What is the origin of anodyne?

Anodyne has a surprising etymology. Its Greek original, anṓdynos “painless,” breaks down to the elements an-, ṓd-, -yn-, -os-. The first element, an- “not,” is from the same Proto-Indo-European source as Latin in- and Germanic (English) un-. The second to last element -yn- is from the noun suffix -ýnē; the last element, -os, is an adjective ending. The main element odýnē “pain” (édyna in the Aeolic dialect) consists of ṓd-, a derivative of the Greek root ed-, od- from the Proto-Indo-European root ed-, od- “to eat” (source of Latin edere, Germanic (Old English) etan, Hittite et-, Homeric Greek édmenai, all meaning “eat, to eat.”) In Greek odýnē is something that eats you (cf. colloquial English, “What’s eating you?”). The Germanic languages also have the compound verb fra-etan “to eat up, devour,” which becomes in German fressen “devour, gorge, corrode,” and in Old English fretan “to devour,” English fret, which nowadays usually has only its extended sense “feel worry or pain.” Anodyne entered English in the 16th century.