Molder, Moulder, v. i. [imp. & p. p. Moldered or Mouldered; p. pr. & vb. n. Moldering or Mouldering.]
Etymology: [From Mold fine soft earth: cf. Prov. G. multern.]
To crumble into small particles; to turn to dust by natural decay; to lose form, or waste away, by a gradual separation of the component particles, without the presence of water; to crumble away. The moldering of earth in frosts and sun. Bacon. When statues molder, and when arches fall. Prior. If he had sat still, the enemy's army would have moldered to nothing. Clarendon.
2 other Webster entries under this spelling
Molder, Moulder, n.
One who, or that which, molds or forms into shape; specifically (Founding), one skilled in the art of making molds for castings.
Molder, Moulder, v. t.
To turn to dust; to cause to crumble; to cause to waste away. [Time's] gradual touch Has moldered into beauty many a tower. Mason.
Shades of meaning
Fernald has no entry of its own for molder; he lists it under decay.
He lists it without comment; the entries above explain its neighbors.