Here's why:
* Suffixes are added to the end of a word to change its meaning or grammatical function. For example, "-ing" is a suffix that turns a verb into a present participle (e.g., "walk" becomes "walking").
* Root words are the basic units of meaning in a word. They can stand alone or be combined with prefixes and suffixes. In "wonderful," "wonder" is the root word that carries the core meaning of "something that inspires awe or amazement."
* "Ful" in this case is a suffix that is added to the root word "wonder" to create the adjective "wonderful," meaning "inspiring wonder or amazement."
So, "ful" is a suffix that is added to the root word "wonder" to create the adjective "wonderful." It's not a suffix in itself within the word "wonderful."