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