Meaning

verb droop, sink, or settle from or as if from pressure or loss of tautness

noun a shape that sags

verb cause to sag

originFrom earlier sag, sagg, sack, from Middle English saggen, probably from Middle Low German sacken (“to sink, drift”), ultimately of North Germanic/Scandinavian/Old Norse origin, akin to Old Norse søkkva (“to sink”), from a denasalized derivative of Proto-Germanic *sinkwaną (“to sink”). Cognate with Scots seg (“to sink”), Danish sakke (“to lag behind”), Swedish sacka (“to lag”), Icelandic sakka…

Etymology from Wiktionary, CC BY-SA 3.0