This is the 13230th most frequent Russian word.
многочасовых
"Многочасовых" means "lasting many hours" in English.
In this sentence, 'многочасовых' acts as an adjective describing the debates ('дебатов'), specifying that they were 'many-hour' or 'hours-long'.
Многочасовых дебатов на совещании оказалось недостаточно для принятия решения.
The hours-long debates at the meeting were not enough to make a decision.
Here, 'многочасовых' is used to describe trips ('поездок'), indicating that these trips lasted for multiple hours.
Мы устали от многочасовых поездок по городу в пробках.
We are tired of the hours-long trips through the city traffic.
In this example, 'многочасовых' qualifies discussions ('обсуждений'), emphasizing their extended duration in time.