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to get moldy (mouldy); to get musty; to develop mildew
梅雨のせいでパンがかびてしまった。
The bread got moldy because of the rainy season.
古い本がかびた匂いを放っている。
The old book is giving off a musty smell.
冷蔵庫の奥でチーズがかびていた。
The cheese in the back of the fridge had gone moldy.