This is the 8592nd most frequent Polish word.
przewodniczącego
"Chairman" or "president" (depending on context).
In this sentence, 'przewodniczącego' is used in the accusative case to indicate the person who was elected.
Przewodniczącego wybrano jednogłośnie na zebraniu.
The chairman was elected unanimously at the meeting.
Here, 'przewodniczącego' appears in the accusative case as the direct object of the verb 'znam' (I know).
Nie znam przewodniczącego tej komisji.
I don't know the chairman of this committee.
In this case, 'przewodniczącego' is in the genitive case as it describes ownership of the 'zdania' (opinion).