Synonyms for Decisive:

adj.

aggressive (adjective)
assertive.
all (adjective)
critical.
authoritative (adjective)
definitive.
certain (adjective)
unequivocal, absolute, positive, sure, patent, trusting, confident, indubitable, steadfast, unquestionable, incontrovertible, convinced, doubtless, unmistakable, indisputable, Irrefragable, certain, undoubted, veritable, irrefutable, clear, incontestable, assured, definite, undeniable, set, decided.
definite (adjective)
resolute, firm, peremptory, intent, determined, fateful, strong-minded, assured, conclusive, forceful, resolved, certain, critical, absolute, decided, crucial, definitive, final, set, positive.
final (adjective)
final, conclusive, last, concluding, closing.
positive (adjective)
positive.
resolute (adjective)
determined, spunky, resolved, steely, insistent, uncompromising, valiant, indomitable, ruthless, diligent, steady, implacable, true, intent, persevering, fearless, indefatigable, persistent, unshakeable, decided, constant, strong-willed, thorough, committed, faithful, dauntless, stubborn, headstrong, hearty, set, unbending, bullheaded, tireless, staunch, courageous, unchangeable, relentless, resolute, devoted, serious, plucky, reliable, zealous, steadfast, unwavering, bold, unflinching, tough, stern, strong-minded, firm, willing, dogged, unyielding, tenacious, deliberate, dedicated, iron-willed, loyal, earnest, inexorable.
self-confident (adjective)
sure.
tenacious (adjective)
steadfast, obdurate, spunky, tireless, unflagging, strong-willed, stiff, hard, staunch, tenacious, insistent, dauntless, headstrong, indefatigable, devoted, stubborn, fervent, bullheaded, resolute, enduring, faithful, persistent, persevering, brave, indomitable, courageous, stony, diligent, determined, strong, true, hearty, tough, dogged, bold, undaunted, flintlike, obstinate, plucky, bulldogged.

n.

self-confident, assertive, dignified, self-possessed, self-assured, proud. instrumental, productive, formative, enabling, causal, emphatic, driving, causative, forceful. hot, hotly, hardball, friendly, comfortable, devastating, decide, competitive, handsome. authoritative, definitive. crucial (noun)
definitive.
decisive (noun)
critical, deciding, resolute, peremptory, fateful, conclusive, crucial, determinative, determinant, unhesitating, definite, important, fatal, determining.

Other synonyms:

formative, driving, emphatic. enabling, causative, hardball, causal, authoritative. productive, hotly, instrumental. friendly, competitive, devastating, definitive. handsome. comfortable. hot. crucial
crucial.
Other relevant words:
important, enabling, causative, unhesitating, forceful, deciding, self-confident, authoritative, crucial, hot, hardball, critical, determinative, causal, definitive, formative, fatal, determining, assertive, peremptory, self-assured, friendly, determinant, fateful, decide, competitive.

Usage examples for decisive

  1. The decisive moment had arrived. – The Captain of the Gray-Horse Troop by Hamlin Garland
  2. Mercy advanced to the surgeon, and put the decisive question to him. – The New Magdalen by Wilkie Collins