tr. & intr.v. slack·ened, slack·en·ing, slack·ens
1. To make or become slower; slow down: The runners slackened their pace. Air speed slackened.
2. To make or become less tense, taut, or firm; loosen: I slackened the line to let the fish swim. The sail's sheet slackened as the wind died.
3. To make or become less vigorous, intense, or severe; ease: slacken discipline; afraid that morale might slacken.
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.