Chiefly Brit. rambunctious, boisterous, unruly, etc.
altered (? after rum) < robustious
See rumbustious in American Heritage Dictionary 4
Uncontrollably exuberant; unruly: “Common to both his illustrations and his independent paintings . . . and lurking below their rumbustious surface, is a sympathy for the vulnerability of the ordinary human being”(Christopher Andreae).
Origin: Probably alteration of robustious (influenced by rambunctious)