Late 16th century. From Dutch ritmeester and (in later use) its cognate German Rittmeister, with remodelling of the second element after master. Compare later Rittmeister.
Definition of Rittmaster in US English:
Rittmaster
noun
(A title of) a captain in a cavalry regiment.
Origin
Late 16th century. From Dutch ritmeester and (in later use) its cognate German Rittmeister, with remodelling of the second element after master. Compare later Rittmeister.