Which of the following word is an antonym of the word Orthodox?

Unconventional

The antonym of the word orthodox is unconventional.

• Orthodox means conforming to the traditional or generally accepted way of doing things.
• Unconventional means not conforming to the traditional or generally accepted way of doing things.

The other words do not have opposite meanings to orthodox.

• Usual means happening or done regularly or typically.
• Plentiful means existing or available in large quantities.
• Sound means based on good judgment or common sense; sensible.