"What's the plural of codex?"

Single Examples:

1. The codex contains handwritten texts from the medieval period.
2. He studied the ancient codex to unravel its secrets.
3. She donated a rare and valuable codex to the library.

Plural Examples:

1. The library houses a collection of ancient codices.
2. Many valuable codices were discovered in the archaeological excavation.
3. Researchers are studying the content of these ancient codices.