This is the 16457th most frequent Russian word.
рыбаком
Fisherman.
The word 'рыбаком' is used as an instrumental case noun, describing the occupation or role of 'my grandfather'.
Мой дед был рыбаком всю свою жизнь.
My grandfather was a fisherman all his life.
Here, 'рыбаком' again appears in the instrumental case, this time to convey the role or profession adopted by the subject.
Он стал рыбаком, потому что любит природу.
He became a fisherman because he loves nature.
In this case, 'рыбаком' is used to describe the person the subject met, emphasizing the state or role of the individual in the instrumental case.