Zeal

The most appropriate antonym of the word zeal is apathy.

• Zeal means "great enthusiasm and interest in something."
• Apathy means "lack of interest, enthusiasm, or concern."

The other words do not have the same meaning as "zeal" and are therefore not antonyms.

• Vigor means "great physical or mental energy."
• Enthusiasm means "a feeling of excitement and eagerness."
• Ardor means "great passion or intensity."