Etymology
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each 

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.

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each other 
reciprocal pronoun, originally in late Old English a phrase, with each as the subject and other inflected (as it were "each to other," "each from other," etc.).
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ilk (adj.)
Old English ilca "the same" (pron.), from Proto-Germanic *ij-lik (compare German eilen), in which the first element is from the PIE demonstrative particle *i- (see yon) and the second is that in Old English -lic "form" (see like (adj.)). Of similar formation are each, which and such, but this word disappeared except in Scottish and thus did not undergo the usual southern sound changes. Phrase of that ilk implies coincidence of name and estate, as in Lundie of Lundie; it was applied usually to families, so that by c. 1790 ilk began to be used with the meaning "family," then broadening to "type, sort."
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every (adj.)

"each, considered indefinitely as a unitary part of an aggregate; all, of a collective or aggregate number, taken one by one;" early 13c., contraction of Old English æfre ælc "each of a group," literally "ever each" (Chaucer's everich), from each with ever added before it for emphasis. The word still is felt to want emphasis; as in Modern English every last ..., every single ..., etc.

Also a pronoun to Chaucer, Shakespeare, Spenser, "each of any number of persons or things; every one." Compare everybody, everything, etc. The word everywhen is attested from 1843 but never caught on; neither did everyhow (1837).

Every now and then "repeatedly, at short intervals" is from 1660s. Every once in a while, U.S. colloquial, "now and then, from time to time," is attested from 1814 (Bartlett calls it "A singular though very common expression"). Slang phrase every Tom, Dick, and Harry "every man, everyone" dates from at least 1723, from the common English given names.

That is to ſay, they affirm, that once upon a Time (tho' they never yet could tell when) all Mankind were upon a Level, and that there was no ſuch Thing as Government in the World; and that Tom, Dick, and Harry, ay, every individual Man, Woman, and Child, had a Right to the whole World. [Charles Leslie, "A Short and Eaſie Method with the Deists," London, 1723]
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*aiw- 

also *ayu-, Proto-Indo-European root meaning "vital force, life; long life, eternity."

It forms all or part of: age; aught (n.1) "something; anything;" aye (adv.) "always, ever;" Ayurvedic; coetaneous; coeval; each; eon; eternal; eternity; ever; every; ewigkeit; hygiene; longevity; medieval; nay; never; no; primeval; sempiternal; tarnation; utopia

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit ayu- "life;" Avestan aiiu "age, life(time);" Greek aiōn "age, vital force; a period of existence, a lifetime, a generation; a long space of time," in plural, "eternity;" Latin aevum "space of time, eternity;" Gothic aiws "age, eternity," Old Norse ævi "lifetime," German ewig "everlasting," Old English a "ever, always."  

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respective (adj.)

mid-15c., "relative, having relation or reference to something" (a sense now obsolete), from Medieval Latin respectivus "having regard for," from Latin respect- past-participle stem of respicere "look back at, regard, consider" (see respect (v.)). The meaning "relating or pertaining severally each to each, connected with each of those in question" is from 1640s.

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interflow (n.)
"a flowing into each other," 1839, from inter- + flow (n.).
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semi-monthly (adj.)

also semimonthly, "fortnightly; occurring, issued, etc. twice in each month," 1809, from semi- + monthly.

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crossroad (n.)

also cross-road, 1680s, "road that crosses from one main road to another;" 1719 as "one of two or more roads that cross each other," from cross- + road. Meaning "place where two roads cross each other" is by 1808. Figurative sense "a turning point, a moment of decision" is from 1733.

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astride (adv.)
"with one leg on each side," 1660s, from a- (1) "on" + stride (n.).
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