"sag" is a correct and usable word in written English.
You can use it as a verb meaning to droop, hang down loosely, or become weakened or less intense. Example sentence: The old tree's branches began to sag under the weight of the wet snow.
Both are drawn from reviews in the Sunday Times by Waldemar Januszczak: "Rothko's problem… is the dark myth that he allowed to emerge around him while he was alive… This tremulous Rothko story line presents him as the Melancholy Martyr of Modernism, a deeply pessimistic presence whose painted fogs sag, paradoxically, with tons of heavyweight spirituality… His suicide topped it all off splendidly.
Most companies' stocks would sag on the sort of news Brazil's oil giant has faced in the past three weeks.
That is good news for oil consumers, arising out of bad: the biggest reason why prices have dropped below $20, even as OPEC plans production cuts, is that the world economy is weak and demand is expected to sag further.
Parts of the house will still sag noticeably, but they will be stable.
Leave a grassy patch of it alone and it will eventually sag into a zigzag pattern called "catsteps".
Pupils' blazer lapels sag with enamel badges for choir, language-learning, mentoring younger pupils and so on.
THE long white tent outside the federal courthouse in Manhattan, where the trial of Martha Stewart is drawing to a close, has begun to sag a bit recently.
On Norman Rush's "Mortals": "the novel has the air at times of a once fatter man whose thinner frame is now making his skin sag a bit".
Without them, the economy would sag horribly; yet their work is illegal.
His tactful, patient, encouraging editor at Faber, Charles Monteith, was a lifeline to him, a friend on whom he relied more than any other during the second half of his life.Later chapters sag, perhaps unavoidably, under the weight of Golding's gathering fame and honours the Booker, the Nobel.
