from custom introduced by Pope Gregory the Great of sprinkling ashes on the heads of penitents on the first day of Lent. Meaning "mortal remains of a person" is late 13c., in reference to the ancient custom of cremation.
"tree," O.E. æsc "ash tree," also "spear made of ash wood," from P.Gmc. *askaz, askiz (cf. O.N. askr, O.S. ask, M.Du. esce, Ger. Esche), from PIE base *os- "ash tree" (cf. Arm. haci "ash tree," Alb. ah "beech," Gk. oxya "beech," L. ornus "wild mountain ash," Rus. jasen, Lith. uosis "ash"). Ash
the preferred wood for spear-shafs, so O.E. æsc sometimes meant "spear" (cf. æsc-here "company armed with spears").