'Slack water' definitions:

Definition of 'slack water'

noun

A stretch of water without current or movement; "suddenly they were in a slack and the water was motionless" [syn: slack, slack water]

noun

The occurrence of relatively still water at the turn of the (low) tide [syn: slack water, slack tide]

From: GCIDE

Slack \Slack\, a. [Compar. Slacker; superl. Slackest.] [OE. slak, AS. sleac; akin to OS. slak, OHG. slah, Prov. G. schlack, Icel. slakr, Sw. slak; cf. Skr. s[.r]j to let loose, to throw. Cf. Slake.] Lax; not tense; not hard drawn; not firmly extended; as, a slack rope. [1913 Webster]
2. Weak; not holding fast; as, a slack hand. --Milton. [1913 Webster]
3. Remiss; backward; not using due diligence or care; not earnest or eager; as, slack in duty or service. [1913 Webster]
The Lord is not slack concerning his promise, as some men count slackness. --2 Pet. iii. 9. [1913 Webster]
4. Not violent, rapid, or pressing; slow; moderate; easy; as, business is slack. "With slack pace." --Chaucer. [1913 Webster]
C?sar . . . about sunset, hoisting sail with a slack southwest, at midnight was becalmed. --Milton. [1913 Webster]
Slack in stays (Naut.), slow in going about, as a ship.
Slack water, the time when the tide runs slowly, or the water is at rest; or the interval between the flux and reflux of the tide.
Slack-water navigation, navigation in a stream the depth of which has been increased, and the current diminished, by a dam or dams. [1913 Webster]
Syn: Loose; relaxed; weak; remiss; backward; abated; diminished; inactive; slow; tardy; dull. [1913 Webster]