Greek-derived nouns ending in -on change to -a in the plural form.
Region is regular. It follows the Greek -a rule.
Use plural verbs: "The regia are ready" (not "is ready").
Yes. The plural regia is standard across all English variants.
The word region follows the standard English pluralization rule. When forming the plural, region becomes regia. This follows the Greek -a pattern, which is one of the most common plural rules in English.
Understanding why region becomes regia helps with spelling and pronunciation. Greek-derived nouns ending in -on change to -a in the plural form.
When using regia in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The regia are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.