ash (n.1)

"powdery remains of fire," Old English æsce "ash," from Proto-Germanic *askon (source also of Old Norse and Swedish aska, Old High German asca, German asche, Gothic azgo "ashes"), from PIE root *ai- (2) "to burn, glow" (source also of Sanskrit asah "ashes, dust," Armenian azazem "I dry up," Greek azein "to dry up, parch," Latin ardus "parched, dry"). Spanish and Portuguese ascua "red-hot coal" are Germanic loan-words.

Symbol of grief or repentance; hence Ash Wednesday (c. 1300), from custom introduced by Pope Gregory the Great of sprinkling ashes on the heads of penitents on the first day of Lent. Ashes meaning "mortal remains of a person" is late 13c., in reference to the ancient custom of cremation. Meaning "Finely pulverized lava thrown from a volcano" is from 1660s.

ash (n.2)

popular name of a common type of forest tree of Eurasia, North America, and North Africa, Old English æsc "ash tree," from Proto-Germanic *askaz, *askiz (source also of Old Norse askr, Old Saxon ask, Middle Dutch esce, German Esche), from PIE root *os- "ash tree" (source also of Armenian haci "ash tree," Albanian ah "beech," Greek oxya "beech," Latin ornus "wild mountain ash," Russian jasen, Lithuanian uosis "ash").

The close-grained wood of the ash is tough and elastic, and it was the preferred wood for spear-shafts, so Old English æsc sometimes meant "spear," as in æsc-here "company armed with spears," æsc-plega "war," literally "spear-play." Æsc also was the name of the Old English runic letter that begins the word.