Spelling variants in French that were brought over into Middle English account for parallels such as ensure/insure, and most en- words in English had at one time or another a variant in in-, and vice versa
'Portable' heritage and communities in transit (research conducted in conjunction with the research group Circulation and Place-Making). Word-forming element meaning "near, at, in, on, within," from Greek en "in," cognate with Latin in (from PIE root en "in"), and thus with en- (1). Also used with native and imported elements to form verbs from nouns and adjectives, with a sense "put in or on" (encircle), also "cause to be, make into" (endear), and used as an intensive (enclose).
"sentence passed by the Inquisition" (plural autos-da-fé), 1723, from Portuguese auto-da-fé "judicial sentence, act of the faith," especially the public burning of a heretic, from Latin actus de fide
Also source of Italian festa, Spanish fiesta), from Latin festa "holidays, feasts, festal banquets," noun use of neuter plural of festus "festive, joyful, merry," related to feriae "holiday" and fanum "temple," from Proto-Italic fasno- "temple," from PIE dhis-no- "divine, holy.
The first element possibly from da, Doric form of Greek gē "earth" (see Gaia), but Liddell & Scott find this "improbable" and Beekes writes, "there is no indication that da means 'earth', although it has also been assumed in the name of Poseidon. Suffix added to nouns to produce adjectives meaning "made of, of the nature of" (such as golden, oaken, woolen), corresponding to Latin -anus, -inus, Greek -inos.
Word-forming element making verbs (such as darken, weaken) from adjectives or nouns, from Old English -nian, from Proto-Germanic -inojan (also source of Old Norse -na), from PIE adjectival suffix -no-. In Greek religion, the Olympian goddess of agriculture and useful vegetation, protectress of the social order and of marriage, mother of Persephone, from Greek Dēmētēr. 1300, "religious anniversary characterized by rejoicing" (rather than fasting), from Old French feste "religious festival, holy day.