A person who is property of another and bound to serve him

One word substitute is Slave.

Bondsman: a person who stands surety for a bond.
Slave: (especially in the past) a person who is the legal property of another and is forced to obey them.
Servant: a person who performs duties for others, especially a person employed in a house on domestic duties or as a personal attendant.
Subordinate: lower in rank or position.