IPA: /bɪˈsiːdʒər/
KK: /bɪˈsiːdʒər/
A person who surrounds a place, such as a city or fortress, in order to capture it or force its surrender.
The besieger set up camp outside the city walls, preparing for a long siege.
Besieger → It is formed from "be-" (meaning about or around) and "siege" (from Old French *sege*, meaning to sit or to besiege). The word "besieger" refers to someone who surrounds or lays siege to a place, typically in a military context.
Think of someone who is 'surrounding' ('be-') a place to 'sit' ('siege') and take control — that's what a besieger does.