I often hear one adjective used when the other adjective is the appropriate one.

Problem:
The adjectives “jealous” and “envious” are not exactly synonyms.

Explanation:
The adjective “jealous” means feeling uneasiness toward another person because of resentment of that person’s success or from suspicion or fear of rivalry.

The adjective “envious” means feeling covetous toward another person’s possessions.

I often hear American English speakers use “jealous” when they mean “envious” instead.

I believe that the use of “jealous” when “envious” is the right adjective is consistent with my “Devolution toward Simpler” hypothesis. It’s simpler to say the two-syllable “jealous” than to say the three-syllable “envious”.

Solution:
Use “jealous” when talking about one person’s attitude toward another person. Use “envious” when talking about one person’s attitude toward another person’s possessions.