Is envious a suffix or prefix?

"Envious" is neither a suffix nor a prefix. It's a complete word meaning "feeling or showing envy."

* Suffixes are added to the end of a word to modify its meaning (e.g., -ness, -ly, -ing).

* Prefixes are added to the beginning of a word to modify its meaning (e.g., un-, pre-, re-).

The word "envious" itself is derived from the noun "envy," but it's a standalone adjective.