vassal

Short definition from Wiktionary

Noun

1. 1
   The grantee of a fief, a subordinate granted use of a superior's land and its income in exchange for vows of fidelity and homage and (typically) military service.
2. 2
   Any direct subordinate bound by such vows to a superior.
3. 3
   Any subordinate bound by similar close ties.

Adjective

1. 1
   Resembling a vassal; slavish; servile.

Verb

1. 1
   To treat as a vassal or to reduce to the position of a vassal; to subject to control; to enslave.
2. 2
   To subordinate to someone or something.