According to vocabulary.com, zealous is an adjective that means great interest in something. It comes from the noun zeal.
- The city council was zealous in its attempt better the community.
- Mary held zealous contempt for her rival.
- The city showed how zealous it could be for its citizens.
- Her zealous behavior made the party a smash.
Some synonyms include ardent, avid, dedicated, and earnest.