56 synonyms for ambitious such as challenging, aggressive, arduous, and bold. Ambitious is an adjective, and its antonyms are unambitious and lazy.
Aggressive, anxious, aspiring, assertive, avid, committed, desirous, determined, driven, dying, eager, energetic, enterprising, enthusiastic, forceful, go-ahead, go-getting, hankering, hoping, hungry, impatient, intent on, itching, longing, motivated, on the make, pioneering, power-hungry, progressive, purposeful, pushy, raring, striving, wishing, yearning, and zealous.
Arduous, bold, challenging, demanding, difficult, exacting, extravagant, formidable, grandiose, hard, hellish, killing, knackering, monumental, onerous, stiff, strenuous, toilsome, and tough.