(Latin: in, into, within, inside, on, toward [il-, ir-, im-], in, into, etc.: involve, incur, invade; also, used intensively, as in the words inflame and inflammable, or without perceptible force.)

The in- changes or is assimilated to il- before l, as with "illuminate", to im- before b, as with "imbibe"; before m, as with "immediate"; before p, as with "implant"; and to ir- before r, as with "irrigate".

The form generally remains unassimilated in words formed in English; such as, inbreed.

Don't confuse this in-2, meaning "in, into, within", etc. with the Latin prefix in-1 meaning "not" nor with the prefix for English-origin words in-3 meaning "in, into; within".