to become less.

to make less; reduce.

Archaic . to represent as less; depreciate; disparage.

verb

enlarge , extend , increase , raise , strengthen

verb

abate , abridge , amputate , attenuate , become smaller , clip , close , contract , crop , curtail , cut , cut back , decline , decrease , de-escalate , degrade , die down , dilute , diminish , downsize , drain , dwindle , ease , erode , grow less , impair , lighten , minify , minimize , mitigate , moderate , narrow , roll back , shrink , slacken , slack up , slow down , soft-pedal * , take the bite out , take the edge off , take the sting out , taper , taper off , thin , truncate , weaken , wind downnotes:lessen means to decrease in size , extent , or range , while a lesson is a unit of instruction , ebb , let up , peter , rebate , reduce , tail away , allay , alleviate , assuage , comfort , palliate , abbreviate , adulterate , bate , belittle , compress , condense , constrict , cut down , demote , deplete , depreciate , disparage , extenuate , lower , mollify , pare , plummet , recede , relieve , retrench , slump , soften , subside , temper , wane , whittle