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.