Simple Definition:
A suffix is a group of letters added to the end of a word to change its meaning or grammatical function [grammatical function refers to how the word is used in a sentence]. For example, the suffix -ful added to the word “beauty” creates the word “beautiful,” and the suffix -able added to the word “read” creates the word “readable.”
Very Simple Definition:
A suffix is a group of letters added to the end of a word to change its meaning or how it is used in a sentence. For example, adding -ful to “beauty” makes “beautiful,” and adding -able to “read” makes “readable.”