Based on Wikipedia article, in linguistics, declension is the inflection of nouns, pronouns, adjectives, and articles to indicate number (at least singular and plural), case (nominative or subjective, genitive or possessive, etc.), and gender.
Declension is a noun. What is a proper verb to say "I want to say different words that appeared from the word day - days, daily etc". How to say it in one word in English?