/ ˈslækən; NAmE / verb
1.
slacken sth to gradually become, or to make sth become, slower, less active, etc.
SYN relax :
[ v ]
We've been really busy, but things are starting to slacken off now.
[ vn ]
She slackened her pace a little (= walked a little more slowly) .
2.
to become or to make sth become less tight
SYN loosen :
[ v ]
His grip slackened and she pulled away from him.
[ vn ]
He slackened the ropes slightly.