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