Longman Dictionary of Contemporary English
The Collaborative International Dictionary
In- \In-\ ([i^]n-). [L. in-; akin to E. un-. See Un-.] An inseparable prefix, or particle, meaning not, non-, un- as, inactive, incapable, inapt. In- regularly becomes il- before l, ir- before r, and im- before a labial.
In- \In-\ ([i^]n-). [See In, prep. Cf. Em-, En-.] A prefix from Eng. prep. in, also from Lat. prep. in, meaning in, into, on, among; as, inbred, inborn, inroad; incline, inject, intrude. In words from the Latin, in- regularly becomes il- before l, ir- before r, and im- before a labial; as, illusion, irruption, imblue, immigrate, impart. In- is sometimes used with an simple intensive force.
Douglas Harper's Etymology Dictionary
prefix meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant), from Latin in- "not," cognate with Greek an-, Old English un-, from PIE *ne "not" (see un- (1)).
element meaning "into, in, on, upon" (also im-, il-, ir- by assimilation of -n- with following consonant), from Latin in- "in" (see in). In Old French this often became en-, which usually was respelled in English to conform with Latin, but not always, which accounts for pairs like enquire/ inquire. There was a native form, which in West Saxon usually appeared as on- (as in Old English onliehtan "to enlighten"), and some verbs survived into Middle English (such as inwrite "to inscribe"), but all now seem to be extinct. Not related to in- (1) "not," which also was a common prefix in Latin: to the Romans impressus could mean "pressed" or "unpressed."
Etymology 1 alt. Prefixed to certain words to give the senses of in, into, towards, within. pre. Prefixed to certain words to give the senses of in, into, towards, within. Etymology 2
pre. in, into Etymology 3
pre. 1 (context non-productive English) Used with certain words to reverse their meaning 2 # (context non-productive English) Added to adjectives to mean ''not'' 3 # (context non-productive English) Added to nouns to mean ''lacking'' or ''without''
Usage examples of "in-".
The very qualities that had been a hindrance, if not actually harmful, to him in the world he had lived in- his strength, his disdain for the comforts of life, his absent-mindedness and simplicity- here among these people gave him almost the status of a hero.