This is the 16783rd most frequent Russian word.
случайным
"Случайным" means "random" or "accidental" in English.
This word 'случайным' is used as an adjective describing the outcome in the instrumental case, reflecting it happened by chance.
Этот результат был случайным.
This result was random.
Here, 'случайным' serves as an adjective describing a temporary partner in the instrumental case, indicating the pairing occurred randomly.
Его случайным напарником оказался известный актер.
His random partner turned out to be a famous actor.
In this sentence, 'случайным' is part of an adverbial phrase 'случайным образом', illustrating the manner in which the book was discovered randomly.