This is the 8249th most frequent Russian word.
марафонский
Marathon-related; pertaining to a marathon.
Here, 'марафонский' is used as an adjective to describe the type of the run, indicating its association with a marathon.
Трудно было выдержать марафонский забег длиной в 42 километра.
It was challenging to endure the marathon-length run of 42 kilometers.
In this sentence, 'марафонский' metaphorically conveys the prolonged nature of the discussion, likened to the duration of a marathon.
Обсуждение проекта затянулось на марафонский срок, продолжавшийся несколько недель.
The discussion of the project stretched into a marathon-like duration, lasting several weeks.
Here, 'марафонские' describes the intense and sustained efforts metaphorically by comparing them to the rigors of a marathon.