What does the prefix im- and e-mean?

The prefix 'im' means 'not'.

Confusion arises from the assimilation of this old definition of im-, into the present English definition meaning not. Il-, im- and ir- are all presently defined as auxiliary prefixes of in-.

• il- is used for Words beginning with L; illegal.

• im- is used for Words beginning with B, P or M; imbalance, impenetrable and immortal.

• ir- is used for Words beginning with R; irregular.