underking
An inferior or subordinate king; a viceroy.
From the Johore capital on the island of Pulau Penyengat in the Riau Archipelago, where Parani's brother became "underking" to a puppet Malay sultan, the Bugis extended their control over the tin negeri of Kedah and Perak, [...]
Where it comes from
From Middle English underking, from Old English undercing, undercyning (“under-king, viceroy”), possibly from Proto-West Germanic *underkuning, from Proto-Germanic *underkuningaz, equivalent to under- + king. Cognate with Dutch onderkoning (“viceroy”), German Unterkönig (“underking”), Danish underkonge (“underking”), Swedish underkung (“underking”).
Adapted from the Wiktionary entry underking (CC BY-SA 4.0).