Possessing gumption; showing initiative, resourcefulness, and courage; characterized by common sense and decisive action.
From 'gumption' plus the adjectival suffix '-ous,' though 'gumptious' is a back-formation and less common than the noun. The creation of this adjective is somewhat modern and informal.
Interestingly, 'gumptious' is a back-formation—people made it FROM the noun 'gumption' by removing what they thought was a suffix, showing how language evolves as speakers invent words that seem like they should exist.
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