Definition of "moulder"

[Time's] gradual touch / Has moulder'd into beauty many a tower.

1772–1782, William Mason, The English Garden

And when the public, which has not been insensible to the merits of "Sense and Sensibility," "Pride and Prejudice," "Mansfield Park," and "Emma," shall be informed that the hand which guided that pen is now mouldering in the grave, perhaps a brief account of Jane Austen will be read with a kindlier sentiment than simple curiosity.

1817 December 20 (date written), Biographical Notice of the Author; published in Northanger Abbey: And Persuasion. […], volume I, London: John Murray, […], 20 December 1817 (indicated as 1818), page v

The day is cold, and dark, and dreary; / It rains, and the wind is never weary; / The vine still clings to the mouldering wall, / But at every gust the dead leaves fall, / And the day is dark and dreary.

1842, Henry Wadsworth Longfellow, “[Miscellaneous.] The Rainy Day.”, in Ballads and Other Poems, 2nd edition, Cambridge, Mass.: […] John Owen, stanza 1, page 111

John Brown's body lies a-mouldering in the grave, but his soul goes marching on!

c. 1855, John Brown’s Body

Today the trackbed moulders, although Lancashire council reports that it's largely intact to around 1.5 miles south of Fleetwood.

2022 January 12, Philip Haigh, “Okehampton should be the start of railway restoration”, in RAIL, number 948, page 50

It was, however, most interesting work, and the moulders themselves were a decent crowd, never tired of making jokes about themselves such as the hoary one that moulders did not live long, which however ran counter to the other one that no germs could live in a foundry—the atmosphere was too foul.

1944 November and December, A Former Pupil, “Some Memories of Crewe Works—II”, in Railway Magazine, page 342