General Antonyms:
* Apathetic: Lacking interest or enthusiasm.
* Indifferent: Not caring about something.
* Lackadaisical: Lacking enthusiasm and effort.
* Halfhearted: Showing little enthusiasm or interest.
* Passive: Not taking an active part.
* Uninterested: Not wanting to know or be involved.
Antonyms related to specific contexts:
* Reluctant: Unwilling to do something. (If someone is zealous about working, they might be reluctant to take a break).
* Hesitant: Uncertain about doing something. (If someone is zealous about trying new things, they might be hesitant to try something dangerous).
* Cautious: Careful to avoid risks. (If someone is zealous about achieving a goal, they might be cautious in their approach).
* Dismissive: Showing that something is unimportant. (If someone is zealous about a cause, they might be dismissive of opposing views).
The best antonym will depend on the specific meaning of "zealous" in the context you are using it.