This is the 14718th most frequent Russian word.
пессимистом
A pessimist.
Here, 'пессимистом' is in the instrumental case, expressing the state or role that he might embody.
Даже в трудные времена он никогда не становится пессимистом.
Even in difficult times, he never becomes a pessimist.
The word 'пессимистом' is used in the instrumental case to indicate the role or characteristic described in the context.
Он всегда был известен как пессимистом среди своих друзей.
He has always been known as a pessimist among his friends.
The word 'пессимистом' is used as a predicate nominative in the instrumental case following the verb 'назвать'.