1 remiss, careless, indolent, negligent, lax, lazy, idle, neglectful, delinquent, inattentive, otiose, dilatory, cunctatory, laggard, easygoing, slothful, sluggish, lethargic, shiftless, do-nothing, fainéant, Colloq asleep at the switch or the wheel, asleep on the job:
Production has fallen off because the workers are getting slack.
2 loose, flabby, flaccid, soft, limp, baggy, drooping, droopy, bagging, sagging, floppy:
The flag hung down, slack in the still air.
3 Often, slack or slacken off or up.
(a) let go, let run, let loose, release, slacken, loose, loosen, relax, ease (out or off), let up (on):
Slack off the stern line a bit.
(b) slow (down or up), delay, reduce speed, tire, decline, decrease, diminish, moderate, abate, weaken:
Barnes could not keep up his terrific pace and is beginning to slack off. Business has slackened off since Christmas
4 neglect, shirk, Colloq Brit skive (off), US goof off, Chiefly military gold-brick, Taboo Slang US fuck the dog:
Don't let the foreman find you slacking.
5 lull, pause, inactivity, cut-back, lessening, reduction, abatement, drop-off, downturn, diminution, decline, fall-off, decrease, dwindling:
How do you compensate for the slack in sales of ski equipment during the summer?
6 room, looseness, slackness, play, give:
There's too much slack in that mooring line.