en-1 pref. repr. (O)F. en-, the form assumed by the L. prefix IN-1; before b and p and occas. before m it takes the form EM-1, but this was not established in Eng. sp. before XVII, enb-, enp- being more frequent than emb-, emp- in ME., as in OF. From an early date IN-1, IM-1 have been substituted for en-, em-, and vice versa, the former being gen. preferred in XVII; in some words (e.g. em-, imbed, en-, inclose) both are still current; in others (e.g. impair, inquest) im-, in- have replaced em-, en-, where these are historically appropriate; in ensure and insure the variants have been allocated to different meanings. As a living formative (from XIV) en- has been used in senses mainly identical with those of L. IN-1: viz. put in, into, or on (something), as encase, enthrone; bring or come into a certain state, as enable, endear; with emphatic or neutral force, as enlighten, enliven.

en-2 repr. Gr. en-, the prep. en IN used as prefix, as in endemic, energy; before b, m, p, ph it takes the form EM-2; before l it becomes el- (as in ellipse).

en- The French en, meaning ‘in’, used as a prefix meaning ‘in’, ‘into’, or ‘inside’.

en- From the French en meaning ‘in’, a prefix meaning ‘in’, ‘into’, or ‘inside’.

en- (em-) prefix denoting in; inside.