slake (v.)

Middle English slak, of persons, "indolent, lazy;" also (from c. 1300), of things or parts, "loose, not tight or taut;" from Old English slæc "remiss, lax, characterized by lack of energy, sluggish, indolent, languid; slow in movement, gentle, easy," from Proto-Germanic *slakas (source also of Old Saxon slak, Old Norse slakr, Old High German slah "slack," Middle Dutch lac "fault, lack"), from PIE root *sleg- "be slack, be languid" (languid is an IE cognate of it).

As an adverb from late 14c. Slack-key in reference to guitar tunings with looser strings (1975) translates Hawaiian ki ho'alu. Slack water (n.) is from 1769 as "time when tide (high or low) is not flowing" (slake-water is from 1570s); as "part of a river behind a dam" by 1836, especially American English.

Formerly common in depreciative compounds such as slack-jawed (q.v.), slack-handed "remiss, negligent" (1670s). Slack-baked "baked imperfectly, half-baked" is from 1823; used figuratively from 1840. The 17c. had slack-hammed. Slack and slow was a Middle English alliterative pairing.

1510s, transitive, "to moderate, make slack," a back-formation from slack (adj.) after the original verb in this sense, slake (q.v.), veered into a specialized sense.

The intransitive meaning "be slack; be remiss, inactive, or idle; fail to exert oneself" is attested from 1540s; current use in this sense is probably a re-coining from c. 1904 (see slacker, and compare Old English slacful "lazy," sleacmodnes "laziness"). Related: Slacked; slacking.

1570s, "cause to become slower;" 1610s, intransitive, "become lax, remiss, or less energetic;" from slack (adj.) + -en (1). Formed after the sense specialization of slake (v.). Related: Slackened; slackening.