IPA: /ˈriːvər/
KK: /ˈrivər/
A person who takes something away by force, often used to describe someone who plunders or steals.
The reaver attacked the village at dawn, taking whatever they could find.
Reaver originates from Old English 'reafian' (meaning to rob or plunder) and the suffix '-er' (meaning a person who). A reaver is thus a person who robs or plunders.
Think of someone who 'robs' ('reafian') — that's why a reaver is a person who takes things by force.