forslack

verb2

1. •
   (rare) To slack up; be or grow slack; pall.
2. •
   (no longer used) To be slack in; neglect by idleness; relax; render slack; delay; lose or spoil by slackness.

   • But they were virgins all, and love eschewed / That might forslack the charge to them fore-shewd. — 1590