1778, an arbitrary formation, part of what Farmer describes as "A class of colloquialisms compounded with an intensive prefix" (ram- or rum-), probably suggesting in part rum (adj.) in its old slang sense of "good, fine," and ramp (n.2). In this case apparently suggested by boisterous, robustious, bumptious, etc. Coined about the same time were rumbustical, rambumptious "conceited, self-assertive," ramgumptious "shrewd, bold, rash," rambuskious "rough," rumstrugenous. Also compare ramshackle, rambunctious.
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