en-1 Also em-.
[French, from Latin in-.]
The prefix can be added to nouns, adjectives, and verbs. Em- is a variant used before the consonants b, m, and p.
One set suggests putting something into or on another (embed, enshrine, enthrone); others have a sense of confining or restricting (ensnare, entwine), or of surrounding something or placing it within something (embrace, enclose, encapsulate, encircle, enfold, engulf, envelop). A large group has a broad sense of ‘put into some state or condition’: embarrass, embitter, encode, endanger, enlarge, enrage, enrich, enslave, entreat. Rarely, it can suggest going into or on to something, as in enplane. Some are figurative terms derived from French or Latin roots, in which the origin of the meaning is no longer easily recognisable: emphasize, endeavour, ensure, endure.
Some words in en- and em- actually contain a variant of ex-1: emancipate is from Latin mancipium, slave; enunciate from Latin nuntius, a messenger; ennervate from Latin nervus, a sinew.
See also in-2, particularly for words that can be spelled both en- and in-.