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