slack: [OE] In common with Dutch and Swedish slak, slack comes from a prehistoric Germanic *slakaz. This was derived from the same ultimate source that produced Latin laxus ‘loose’ (source of English lax, relax, release, and relish) and languēre ‘languish’ (source of English languish). The plural noun slacks was first used for ‘trousers’ in the early 19th century. (The noun slack ‘small pieces of coal’ [15] is a different word, probably borrowed from Middle Dutch slacke ‘waste produced by smelting metal’.) => languish, lax, relax, release, relinquish