mettlesome (adj.)

• active
• acute
• aggressive
• animated
• brisk
• courageous
• dauntless
• dynamic
• edgy
• emotional
• energetic
• enterprising
• enthusiastic
• eruptive
• excitable
• explosive
• fiery
• forceful
• forcible
• game
• gamy
• gritty
• gutsy
• hearty
• high-spirited
• high-strung
• impetuous
• incisive
• inflammable
• intense
• irascible
• irritable
• keen
• kinetic
• lively
• living
• lusty
• nervous
• nervy
• peppery
• peppy
• pertinacious
• perturbable
• plucky
• prickly
• red-blooded
• resolute
• robust
• sensitive
• skittish
• snappy
• spanking
• spirited
• spunky
• strenuous
• strong
• tenacious
• touchy
• tough
• trenchant
• vibrant
• vigorous
• vivacious
• vivid
• volcanic
• zestful
• zesty
• zippy