Emily Dickinson Lexicon

IN, adv. [a prefix, L. in.]

Used in composition as a particle of negation, like the English un, of which it seems to be a dialectical orthography; or it denotes within, into, or among, as in inbred, incase; or it serves only to augment or render emphatical the sense of the word to which it is prefixed, as in inclose, increase. In, before l, is changed into il, as in illusion; and before r, into ir, as in irregular; and into im, before a labial, as in imbitter, immaterial, impatient.