A word is composed of one or more morphemes (the smallest unit of the meaning of a word but that can not stand on its own), and these morphemes may be divided into root words (which hold the most basic meaning of a word), prefixes (Added before a root word) and suffixes (Added at the end of a root word).
The word "unreasonable" has all three types of morphemes:
"Un" is the prefix and it means not, reverse action, deprive of, release from.
"Reason" is the root word and it means "a sufficient ground of explanation or of logical defense."
"Able" is the suffix and it means capable of, susceptible of, fit for, tending to or given to.
A root word has no prefix or suffix and is the most basic part of a word. The prefix of the word 'unreasonable' is 'un'. The root word is 'reasonable.'
