The root word for the word illegal is legal.
Notice the prefix il- in illegal. Prefixes are words, letters or some
numbers that placed before the word itself.
In this case, il- is the prefix of illegal, which means not acquired or
done in a moral or official manner contrary to legal, which is the opposed
definition of illegal.
Examples of prefixes include, re- in remake, re-establish, retake. Notice
the root words, make, establish and take in the given words.
