Prefix: a group of letters that come at the beginning of a word. Root: the basic part of a word; the prefixes and suffixes are added to it. Suffix: a group of letters that come at the end of a word. un + change + able = unchangeable. Some words are just root words, meaning they don't have a prefix or suffix.
Persistent comes from the Latin verb persistere which means "to continue with strength." A persistent salesman refuses to give up.
