word-forming element meaning "in; into," from French and Old French en-, from Latin in- "in, into" (from PIE root *en "in"). Typically assimilated before -p-, -b-, -m-, -l-, and -r-. Latin in- became en- in French, Spanish, Portuguese, but remained in- in Italian.
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). 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.
c. 1300, corage, "heart (as the seat of emotions)," hence "spirit, temperament, state or frame of mind,"from Old French corage "heart, innermost feelings; temper" (12c., Modern French courage), from Vulgar Latin *coraticum (source of Italian coraggio, Spanish coraje), from Latin cor "heart" (from PIE root *kerd- "heart").
Meaning "valor, quality of mind which enables one to meet danger and trouble without fear" is from late 14c. In this sense Old English had ellen, which also meant "zeal, strength." Words for "heart" also commonly are metaphors for inner strength.
In Middle English, the word was used broadly for "what is in one's mind or thoughts," hence "bravery," but also "wrath, pride, confidence, lustiness," or any sort of inclination, and it was used in various phrases, such as bold corage "brave heart," careful corage "sad heart," fre corage "free will," wikked corage "evil heart."
The saddest thing in life is that the best thing in it should be courage. [Robert Frost]
As a general rule, Providence seldom vouchsafes to mortals any more than just that degree of encouragement which suffices to keep them at a reasonably full exertion of their powers. [Hawthorne, "House of Seven Gables"]