the usual Old English word for "river, running water" (still in use in Lancashire, according to OED), from Proto-Germanic *ahwo- (source also of Old Frisian a, Old Saxon aha, Old High German aha, German ahe-, Old Dutch aha, Old Norse "water"), from PIE root *ekweh- "water" (see aqua-). "The standard word in place-names for river denoting a watercourse of greater size than a broc or a burna" [Cambridge Dictionary of English Place-Names].

Old English ælc (n., pron., adj.) "any, all, every, each (one)," short for a-gelic "ever alike," from a "ever" (see aye (adv.)) + gelic "alike" (see like (adj.)). From a common West Germanic expression *aina-galīk (source also of Dutch elk, Old Frisian ellik, Old High German iogilih, German jeglich "each, every"). Originally used as we now use every (which is a compound of each) or all; modern use is by influence of Latin quisque. Modern spelling appeared late 1500s. Also see ilk, such, which.

late 13c., "strenuous, ardent, fierce, angry," from Old French aigre "sour, acid; harsh, bitter, rough; eager greedy; lively, active, forceful," from Vulgar Latin *acrus (source also of Italian agro, Spanish agrio), from Latin acer "keen, sharp, pointed, piercing; acute, ardent, zealous" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").

Meaning "full of keen desire" (early 14c.) seems to be peculiar to English. The English word kept a secondary meaning of "pungent, sharp-edged" till 19c. (as in Shakespeare's "The bitter clamour of two eager tongues," in "Richard II"). Related: Eagerly; eagerness. Eager beaver "glutton for work" [OED] is from 1943, U.S. armed forces slang.

"very large diurnal raptorial bird of the genus Aquila," mid-14c., from Old French egle, from Old Provençal aigla, from Latin aquila "black eagle," fem. of aquilus "eagle," often explained as "the dark colored" (bird); see aquiline. The native term was erne.

Golf score sense is by 1908 (according to old golf sources, because it "soars higher" than a birdie). As the name of a U.S. $10 coin minted from 1792 to 1933, established in the 1786 resolution for a new monetary system (but at first only the desperately needed small copper coins were minted). The figurative eagle-eyed "sharp-sighted" (like an eagle) is attested from c. 1600.

"a young eagle," 1570s, from French aiglette, diminutive of aigle (see eagle).

"organ of hearing," Old English eare "ear," from Proto-Germanic *auzon (source also of Old Norse eyra, Danish øre, Old Frisian are, Old Saxon ore, Middle Dutch ore, Dutch oor, Old High German ora, German Ohr, Gothic auso), from PIE *ous- "ear" (source also of Greek aus, Latin auris, Lithuanian ausis, Old Church Slavonic ucho, Old Irish au "ear," Avestan usi "the two ears").

þe harde harte of man, þat lat in godis word atte ton ere & vt atte toþir. [sermon, c. 1250]

In music, "capability to learn and reproduce by hearing," 1520s, hence play by ear (1670s). The belief that itching or burning ears means someone is talking about you is mentioned in Pliny's "Natural History" (77 C.E.). Until at least the 1880s, even some medical men still believed piercing the ear lobes improved one's eyesight. Meaning "handle of a pitcher" is mid-15c. (but compare Old English earde "having a handle"). To be wet behind the ears "naive" is from 1902, American English. Phrase walls have ears is attested from 1610s. French orielle, Spanish oreja are from Latin auricula (Medieval Latin oricula), diminutive of auris.

also eardrum, "tympanic membrane," 1640s, from ear (n.1) + drum (n.).