slacken
verb [ I or T ]
uk/ˈslækən/ us(also slacken off)to become gradually less strong or slower, or to make something do this:
The overall pace of growth slackened.
The message from retailers is that spending has slackened off.
Management promised never to slacken the pace of modernization.
slackening
noun [ S or U ]
There is some slackening in the domestic air express business.