1. Settling a matter or conflict; conclusive: the decisive battle in the war; the decisive piece of evidence in the lawsuit.
2. Characterized by or showing the ability to make decisions quickly and firmly; resolute: a decisive leader.
Synonyms: decisive, conclusive, critical, crucial, definitive, determinative
These adjectives mean determining an outcome or settling an issue with finality: the decisive vote; a conclusive reason; a critical experiment; a crucial moment; a definitive verdict; the determinative battle.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.