leaf mold Syllabification: (leaf mold) (also leafmold)Definition of leaf mold noun 1soil consisting chiefly of decayed leaves. 2a fungal disease of plants in which mold develops on the leaves. The fungus is Fulvia fulva (formerly Cladosporium fulvum), subdivision Deuteromycotina leaf mold in other Oxford dictionaries Definition of leaf mold in the British & World English dictionary