Short adjectives mean 'am/is/are'.
Ћн бћлен. He is sick.
Онќ больнІ. They are sick.
Ї бћлен (больнђ). I am sick.
Those adjectives that have short forms, have four of them, ending in -#, -а, -о, -ы. Like the past tense of verbs, they agree with the Nominative subject of the sentence. Short adjectives have the verbal meaning 'am/is/are'.
Very few adjectives have short forms that are used in ordinary speech, but some, like бћлен 'sick' and увљрен 'sure' are very frequently used.