The prefix in- changes its form to il- before an l; to im- before b, m or p; and to ir- before r. This prefix (and its variations) have two meanings. Tom's inability to whistle always frustrated him. The argument was illogical.

Does the prefix Il mean not?

Recalling that the prefix in can mean “in, on, or not,” let's go through examples of the five forms “in” which in exists “in” English: Il: Examples include: illegal: “not legal;” illogical: “not logical;” and illegible: “not able to be read.” Note how the il spelling is preferable to inlegal, inlogical, or inlegible!

What are words with the prefix il?