Sentence:  The Lyonesse army cautiously advanced into the forest, but came upon no Daut resistance. Cassander's dissatisfaction was compounded by the pulsing pain in his shoulder. He began to curse under his breath. “Where are the <WSD>skulkers</WSD>? Why do they not reveal themselves?” 
Meaning of the word marked with <WSD> tags:  One who stays where they cannot be seen (often in a cowardly way or with the intent of doing harm).