Webster 1913 Edition
A prefix from Eng. prep. in, also from Lat. prep. in, meaning
as,. In words from the Latin, in- regularly becomes il- before l, ir- before r, and im- before a labial;
inroad; incline, inject, intrude
as,. In- is sometimes used with an simple intensive force.
in-; akin to E.
An inseparable prefix, or particle, meaning
un-as, inactive, incapable, inapt. In- regularly becomes il- before l, ir- before r, and im- before a labial.