Is unintentional a root word or base word?

"Unintentional" is not a root word or a base word. It's a compound word made up of the prefix "un-" and the adjective "intentional".

* "Un-" is a prefix meaning "not" or "opposite of."

* "Intentional" is the base word, meaning "done on purpose."

Therefore, "unintentional" means "not done on purpose" or "accidental."