Explanation:

- Zeal, burning enthusiasm, passion: These words describe a strong and vigorous interest or desire for something. They denote a heightened emotional state characterized by enthusiasm or fervor.

- Option 1: Arid

- Means extremely dry or lacking in interest.

- Opposite of passion or enthusiasm.

- Not suitable as a substitute for zeal.

- Option 2: Ardour (Correct Answer)

- Means intense enthusiasm or passion.

- ?? This is the appropriate one-word substitute for zeal.

- Option 3: Arcuate

- Means shaped like a bow.

- Not related to enthusiasm or passion.

- Option 4: Arena

- Refers to a place of competition or activity.

- Does not convey allure or zeal.