Other forms: sagging, sags, sagged
To sag is to sink or bend under weight. The shelf sagged, sagging in the middle, a sagging roof.
It is gradual and central — things sag in the middle, where the load is furthest from the supports. A sagging roof or floor is a structural warning. Figuratively, spirits sag and support sags, meaning they gradually decline. Note saggy; and that the word came from Low German or Scandinavian, from a root meaning to sink.
1verbsagTo sink or bend under weight.
“The old mattress sagged in the middle, and we rolled towards each other all night.”
2verbdeclineTo decline gradually.
“Sales of the magazine have sagged since most readers moved online.”
sag is a sinking under weight.
Middle English saggen probably came from Middle Low German sacken, to sink, ultimately Scandinavian. Sink comes from a related root.
Proto-Germanic
*sankwijaną — to cause to sink
Middle Low German
sacken — to sink, drift
Middle English
saggen
English, today
sag
From earlier sag, sagg, sack, from Middle English saggen, probably from Middle Low German sacken (“to sink, drift”), ultimately of gmq -/Scandinavian/Old Norse - origin, akin to Old Norse søkkva (“to sink”), a denasalized derivative of Proto-Germanic sankwijaną (“to cause to sink”), related to Proto-Germanic sinkwaną (“to sink”). Cognate with Scots seg (“to sink”), Danish sakke (“to lag behind”), Swedish sacka (“to lag”), Icelandic sakka (“to sink”), Faroese søkka (“to sink, drop down, descend, set”), Dutch zakken (“to fall, drop, sink”), German Low German sacken (“to sink”), and German sacken (“to sink”) (from Low German -). Compare also Norwegian Nynorsk sagga (“to walk or move heavily and slowly”).
Etymology from Wiktionary, CC BY-SA