illness illness /ˈɪlnəs/

noun

1. () Impairment of normal physiological function affecting part or all of an organism  ( unwellness , malady , sickness , illness )
   impairment of normal physiological function affecting part or all of an organism
    I'm feeling under the weather and think I might be coming down with an illness
   I'm feeling under the weather and think I might be coming down with an illness