IPA: /ˈslækən/
KK: /ˈslækən/
To make something less tight, intense, or fast; to loosen or slow down.
I slackened the rope to give the boat more room to move.
Past: slackened
Past Participle: slackened
Slacken → It is formed from "slack" (from Old English *slæc*, meaning loose or not tight) and "-en" (a suffix used to form verbs). The word "slacken" means to make something less tight or to loosen it.
Think of something becoming 'loose' ('slack') when you 'make' it less tight ('-en').