c. 1200, worn-down form of Old English alswa "quite so, wholly so," literally "all so" (see also), fully established by c. 1400. Equivalent to so; any distinction in use is purely idiomatic. Related to German als "as, than," from Middle High German also.

Phrase as well "just as much" is recorded from late 15c.; the phrase also can imply "as well as not," "as well as anything else." Phrase as if, in Kantian metaphysics (translating German als ob), introducing a supposition not to be taken literally, is from 1892; as an interjection of incredulity (as if!; i.e. "as if that really could happen") is attested from 1995. It duplicates Latin quasi. Phrase as it were "as if it were so" is attested from late 14c.

also *es-, Proto-Indo-European root meaning "to burn, glow." 

It forms all or part of: ardent; ardor; area; arid; aridity; aril; arson; ash (n.1) "powdery remains of fire;" azalea; potash; potassium.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit asah "ashes, dust;" Hittite hat- "to dry up;" Greek azein "to dry up, parch," azaleos "dry;" Latin aridus "parched, dry," ārēre "to be dry," āra "altar, hearth;" Armenian azazem "I dry up;" Old English æsce "ash," Old High German asca, Gothic azgo "ashes." 

early 15c., from when + as.

ancient southern constellation, 1590s, from Latin āra "altar, hearth," from PIE root *as- "to burn, glow." 

mid-14c., "where;" early 15c. as a conjunction, "in consideration of the fact that, considering that things are so; while on the contrary," from where (in the sense of "in which position or circumstances") + as.

type of flowering shrub, 1753, Modern Latin, coined by Linnaeus from the fem. of Greek azaleos "dry," related to azein "to dry up," probably from PIE root *as- "to burn, glow." The plant thrives in sandy soil.

"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, Middle Dutch asche, Gothic azgo "ashes"), from PIE root *as- "to burn, glow." Spanish and Portuguese ascua "red-hot coal" are Germanic loan-words.

An ancient 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.

1650s, "dry, parched, without moisture," from French aride "dry" (15c.) or directly from Latin aridus "dry, arid, parched," from arere "to be dry," from PIE root *as- "to burn, glow." Figurative sense of "uninteresting" is from 1827. Related: Aridly; aridness.