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.
Old English had lost the pure form of the word; the modern word replaced synonymous ilk. As a pronoun from c. 1300. Colloquial phrase same here as an exclamation of agreement is from 1895. Same difference curious way to say "equal," is attested from 1945.
"a gathering of witches," 1660s, earlier "a meeting, gathering, assembly" (c. 1500); a variant form of covent, cuvent, from Old French covent, convent, from Latin conventus (see convent).
Covent (13c.) also meant "group of men or women in a monastery or convent." The variant form, and the association of this spelling of the word with witches, arose in Scotland but was not popularized until Sir Walter Scott used it in this sense in "Letters on Demonology and Witchcraft" (1830).
Efter that tym ther vold meit bot somtymes a Coven, somtymes mor, somtymes les; bot a Grand Meitting vold be about the end of ilk Quarter. Ther is threttein persones in ilk Coeven; and ilk on of vs has an Sprit to wait wpon ws, quhan ve pleas to call wpon him. I remember not all the Spritis names; bot thair is on called "Swein," quhilk waitis wpon the said Margret Wilson in Aulderne; he is still clothed in grass-grein .... ["Criminal Trials in Scotland," III, appendix, p.606, confession of Issobell Gowdie in Lochloy in 1662]