Synonyms for Mettlesome (same or very similar meaning)
WordNet sense 1 (displaying animation, vigor, or liveliness):
spirited
WordNet sense 2 (willing to face danger):
game, gamey, gamy, gritty, spunky
WordNet sense 3 (possessing or displaying courage; able to face and deal with danger or fear without flinching):
brave, courageous
From the ODE community, based on WordNet
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