(dated) Semi-formal trousers which are less formal than those that are part of a suit but nowadays are considered suitable casualwear in most offices. (Takes a plural verb even when referring to a single pair; may be referred to as a pair of slacks.)

plural of slack

The state of being slack; the quality of having slack. / Vulgarity in West Indian culture. / A subgenre of dancehall music with sexual lyrics.

plural of slackness

plural of Slack

A surname.

Full of laxity; characterised by laxness; relaxed; (by extension) unmotivated, lazy.

With the mouth in an open position and the jaw hanging loosely, especially as indicating bewilderment or astonishment. / (by extension) Unsophisticated or unthinking; dimwitted in appearance.

A large container full of water or oil or brine used by a blacksmith to quench hot metal.

(UK) A cheap fuel consisting of slack (coal dust) and small lumps of coal (nuts); unlike other solid fuel it was not rationed during the period after World War II.