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