The precious paintings were left in the damp basement and slowly moldered away.

moldered 是动词 molder 的过去式，molder 由 mold（霉菌）加后缀 -er 构成，字面意思是"发霉、生霉菌"，引申为"逐渐腐朽、朽烂"的意思。这个词特别强调由于潮湿或缺乏维护而导致的缓慢腐烂过程。