1. To release tension on
2. To make less active or fast; SYN. slacken, slack up.
3. To avoid responsibilities and work, be idle.
4. To be inattentive to, or neglect, as of duties:
5. To cause to heat and crumble by treatment with water, as of lime; SYN. slake.

Flowing with little speed as e.g. at the turning of the tide

1. A cord or rope or cable that is hanging loosely
2. A stretch of water without current or movement
3. The condition of being loose (not taut); SYN. slackness.