A prefix from Eng. preparation. in, in addition from Lat. prep. in, meaning in, into, on, among. In words through the Latin, in- frequently becomes il- before l, ir- before r, and im- before a labial. In- can be used in combination with an simple intensive power.
An inseparable prefix, or particle, indicating perhaps not, non-, un- as, sedentary, incapable, inapt. In- regularly becomes il- before l, ir- before r, and im- before a labial.