Prefix
A prefix signifying in or into, used in many English words, chiefly those borrowed from the French. Some English words are written indifferently with en-or in-. For ease of pronunciation it is commonly changed to em-before p, b, and m, as in employ, embody, emmew. It is sometimes used to give a causal force, as in enable, enfeeble, to cause to be, or to make, able, or feeble; and sometimes merely gives an intensive force, as in enchasten. See In-.
A prefix from Gr. / in, meaning in; as, encephalon, entomology. See In-.
Source: Webster's dictionaryThe prefixes en- and em- are always nasalized. Source: Internet
It comes from the Classical Greek prefix ἐν- main en-, meaning "to put into", and the verb θάλπειν main thalpein, meaning "to heat". Source: Internet