Archaic To make little of; belittle.(verb-transitive)
To become less; decrease. See Synonyms at decrease.(verb-intransitive)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "lessen" in a sentence
"If you have a Marine or Sailor in 1st platoon, don't be surprised if the frequency of your loved ones calls lessen and their e-mails stop altogether."
"But he knew he would have to use some other stuff to kind of lessen the sting of his disagreement with how McCain is handling that situation about a confidential source."
"Nor will they "lessen" it or compromise it in anyway."