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