What is the prefix and root of heed?

The word "heed" doesn't have a prefix. It's a root word itself, meaning "to pay attention to" or "to take notice of".

However, there are related words that use "heed" as a root:

* Heedful: Meaning "paying attention to" or "mindful of".

* Heedless: Meaning "not paying attention to" or "careless".

* Heeder: (An archaic term) Someone who pays attention or takes notice.

So while "heed" itself doesn't have a prefix, it's a root word from which other words are derived.