What rule applies to he word envy?

The Word "envy" is a noun that refers to a feeling of discontent or resentment aroused by someone else's possessions, qualities, or luck. It can also be used as a verb meaning to desire what someone else has. In terms of grammatical rules, "envy" can be used in various contexts, typically as a subject or object in a sentence, and it often takes a preposition, such as "of" when describing what one envies.