slack

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Not tense or taut; loose: synonym: loose.
• adjective Lacking in activity; not busy.
• adjective Moving slowly; sluggish.
• adjective Lacking in diligence or due care or concern; negligent: synonym: negligent.
• adjective Flowing or blowing with little speed.
• adjective Linguistics Pronounced with the muscles of the tongue and jaw relatively relaxed; lax.
• intransitive verb To make looser or less taut.
• intransitive verb To make slower.
• intransitive verb To be careless or remiss in doing.
• intransitive verb To slake (lime).
• intransitive verb To be or become slack.
• intransitive verb To be inactive or avoid work.
• noun A loose part, as of a rope or sail.
• noun A period of little activity; a lull.
• noun A cessation of movement in a current of air or water.
• noun An area of still water.
• noun Unused capacity.
• noun Casual pants that are not part of a suit.
• adverb In a slack manner.
• idiom Slang (cut/give) To make an allowance for (someone), as in allowing more time to finish something.
• noun A mixture of coal fragments, coal dust, and dirt that remains after screening coal.
• noun A small dell or hollow.
• noun A bog; a morass.

from The Century Dictionary.

• In a slack manner; slowly; partially; insufficiently: as, slack dried hops; bread slack baked.
• noun The finer screenings of coal; coal-dirt; especially, the dirt of bituminous coal.
• To become slack or slow; slacken; become slower: as, a current of water slacks.
• To become less tense, firm, or rigid; decrease in tension.
• To abate; become less violent.
• To become languid; languish; fail; flag.
• To make slack or slow; retard.
• To make slack or less tense; loosen; relax: as, to slack a rope or a bandage.
• To relax; let go the hold of; lose or let slip.
• To make less intense, violent, severe, rapid, etc.; abate; moderate; diminish; hence, to mitigate; relieve.
• To be remiss in or neglectful of; neglect.
• To make remiss or neglectful.
• To slake (lime). See slake, transitive verb, 3.
• To cool in water.
• To retard the speed of, as a railway-train.
• noun A sloping hillside.
• noun An opening between hills; a hollow where no water runs.
• noun A common.
• noun A morass.
• Slow in movement; tardy.
• Slow in flow; sluggish or at rest: as, slack water: specifically noting the tide, or the time when the tide is at rest—that is, between the flux and reflux.
• Slow in action; lacking in promptness or diligence; negligent; remiss.