The correct etymology has been published by M. Janda, Purpurnes Meer. Sprache und Kultur der homerischen Welt. Innsbruck 2014, p. 131-143. Χάρμη "battle" is the zero grade of the root found in χρεμετίζω "to whinny". Within Greek, other derivatives are χρόμος· ψόφος ποιός. Οἱ δὲ χρεμετισμός “kind of noise; but for others, whinnying” (Hsch., χ 757), χρόμη· φρυαγμός, ὁρμή, θράσος “neighing, impulse, boldness” (Hsch., χ 753), χρόμις, name of a fish, χρόμαδος (γενύων) (Il. 23.688) ‘gnashing’, as well as words meaning ‘to cough’ in the medical vocabulary. The PIE root is *ghrem- ‘to thunder, to rumble’, with cognates in Baltic and Slavic: Lith. grumė́ti ‘to thunder’, OCS grъměti ‘to thunder’, both from *ghr̥m-eh1-, OCS gromъ ‘thunder’, “which formally matches χρόμος” (Beekes, EDG). Other cognates are found in Germanic, Goth. gramjan ‘to get angry’, OHG grim ‘cruel’, gram ‘wrathful’. To quote Beekes, “Germanic has several expressions for anger and grumbling, which must originally have referred to sounds like droning, gnashing the teeth, etc.” and “The same meaning is encountered in Av. graməṇtąm ‘of those who are wrathful to us’.” The original meaning of χάρμη is therefore "battle din" or "war cry, war clamor".