1. One that kills: a disease that was a killer of thousands; a killer of new ideas.
2. Slang Something that is extremely difficult to deal with or withstand: an exam that was a real killer.
1. Causing death or destruction: killer floods.
a. Having impressive or effective power or impact; formidable: had a killer smile; made killer profits.
b. Extremely useful or indispensible: a killer web application.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.