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CaseSingularPlural
Nominativeименительный · кто? что?болезнь болезни the subject: who or what acts
Accusativeвинительный · кого? что?болезнь болезни the direct object of the verb
Genitiveродительный · кого? чего?болезни болезней possession, absence, "of"-phrases
Dativeдательный · кому? чему?болезни болезням the receiver: to or for someone
Instrumentalтворительный · кем? чем?болезнью болезнями the tool or companion: with, by
Prepositionalпредложный · о ком? о чём?болезни болезнях location and topics: in, at, about

Болезнь is a feminine noun; the ending pattern above repeats across most feminine nouns, so every table you learn makes the next one cheaper.

Look up any other word in the Russian declension tool, see where болезнь ranks in the most common Russian words, or start from Russian cases explained if the table above is new territory. More vocabulary lives in Russian words by topic and Russian phrases.

12 forms is a table. Using them is a skill.

Slova drills болезнь and every word like it with typed case endings, checked letter by letter.

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