दुर्धर्षः one who is difficult to encounter, कपिः monkey, सुग्रीववचनात् by the command of Sugriva, चतुर्द्वाराणि the four gates, सर्वाणि all, चन्द्रमाः moon, नक्षत्राणीव stars, पर्यक्रामत moves around.

Sushena, a monkey who is difficult to encounter, went around all the four gates just like the moon goes around stars by the order of Sugriva.