h₂erH-mn̥-
“fitted thing, harmonious arrangement”harmony, harmonious, harmonica
Nominal giving Greek harmonia, English harmony, harmonious, harmonica.
Discussion
The nominal derivative *h₂erH-mn̥- descends from the verbal root *h₂er- "to fit together, to join," and its literal meaning — "a fitted thing, a harmonious arrangement" — radiates outward into an astonishing range of descendants spanning warfare, music, mathematics, and craft. Rix (LIV² 269) reconstructs the verbal base with confidence, and Pokorny (IEW 55–61) documents its extraordinary productivity across every major branch.The most unexpected reflex is English arm in its original sense of "weapon." Old English earm and its Germanic cognates descend from a form meaning "that which is fitted together" — a jointed implement, an assembled tool of war. The Latin cognate arma "weapons, equipment" (always plural, always denoting fitted gear) preserves the same semantic kernel and gave English armament, armor, armada, and army. The shift from "fitted thing" to "weapon" is less strange than it appears: in a world of composite bows, socketed spearheads, and riveted shields, a weapon was precisely a thing fitted together with skill.But *h₂er- equally gave rise to Greek harmonia "joining, agreement, harmony," from which English inherits harmony, harmonic, and the entire musical vocabulary of consonance. Beekes (EDG, s.v. ἁρμονία) traces harmonia to the same *h₂er- base through a nasal derivative parallel to *h₂erH-mn̥-. Latin ars, artis "skill, craft" — source of English art, artisan, artifact — likewise derives from this root, encoding the idea that craft is the act of fitting things properly together. Watkins (AHDIER, s.v. *ar-) unifies these strands elegantly: to arm, to harmonize, and to create art are all expressions of the single Proto-Indo-European intuition that the highest human activity is joining things into their right arrangement.