slack v also slacken (off). Cp OED ~ v 12 (1820 quot). Of an ice-field, to break up into loose pieces.
[1856] 1975 WHITELEY 112 Strong breeze offshore—Ice began to slack. 1866 WILSON 393 Just then a light north-west wind slacked the ice from the north shore of Trinity Bay, by which a boat got from Trinity to Catalina ... and in less than half an hour after the arrival of the boat, the ice again came in and stopped all navigation for ten days more. 1873 Maritime Mo ii, 140 Here the ice slackened; steam was got up. 1901 Christmas Bells 13 As these men worked together they soon carried the instrument to safety, just arriving at the store before the ice commenced to slack. 1916 MURPHY 46 At length, well on in April, the wind changed and the ice slackened off and let them clear. All the ships then started north and cracked on northward for all they were worth. T 43-64 I've seen as high as three hundred schooners huddled together in a harbour waitin' for the ice to slack.
