Lessen

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 down