slack-water I. \ˈ ̷ ̷| ̷ ̷ ̷ ̷\adjective Etymology:slack water 1.: marked by slack water < a slack-water period > 2.: carried on in slack water produced artificially (as by a lock or dam) < slack-water navigation > II. transitive verb : to produce slack water in (as a river) by a construction (as a dam, lock, or jetty)