v. 25B6; verb
he slackened his grip : LOOSEN, release, relax, loose, lessen, weaken.
he slackened his pace : SLOW (DOWN), become/get/make slower, decelerate, slack (up).
the rain is slackening : DECREASE, lessen, subside, ease up/off, let up, abate, slack off, diminish, die down, fall off.
tighten.