This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

adj. Having the power to decide; conclusive.

adj. Characterized by decision and firmness; resolute.

adj. Beyond doubt; unmistakable: a decisive defeat.

adj. Having the power or quality of deciding a question or controversy; putting an end to contest or controversy; final; conclusive.

adj. Marked by promptness and decision.

adj. Having the power or quality of deciding a question or controversy; putting an end to contest or controversy; final; conclusive.

adj. Marked by promptness and decision.

Having the power or quality of determining a question, doubt, contest, event, etc.; final; conclusive; putting an end to controversy: as, the opinion of the court is decisive on the question.

Marked by decision or prompt determination.

n. A decisive thing.

adj. determining or having the power to determine an outcome

adj. characterized by decision and firmness

adj. forming or having the nature of a turning point or crisis

adj. unmistakable

"SESAY: The Iraqi prime minister has announces what he calls a decisive offensive in the northern city of Mosul."

determinant    determinative    fateful    determining    fatal    deciding    peremptory    resolute    unhesitating    crucial   

indecisive   

decisive abstraction   

decided    decidable   

decisively    decisiveness   

decided    conclusive    positive    final   

derisive    divisive    incisive    indecisive   

definite    vigorous    unexpected    disastrous    satisfactory    emphatic    convince