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