In 15-16th c. envegle (rarely enveugle), app. a corruption of an earlier *avegle, aveugle, a. Fr. aveugler to blind, f. aveugle, OFr. also avuegle:-late pop.L. aboculum, f. ab- away from, without + ocul-us eye. The word appears to have been analysed as a-vegle, and this by exchange of prefixes, made en-vegle, as in some other words: cf. enbraid = abraid, enorn = aorn, adorn; cf. esp. L. exemplum, OFr. essample, ME. *esaumple, asaumple, corruptly ensample.
It is probable that some analogy suggested the prefix en-, whence the Latinized in-. The stem-vowel ē is normal: cf. people = Fr. peuple,…