Leaden is a term that is used to describe things that are made of heavy and dull materials, or that are slow, tedious and dull in nature. Synonyms for "leaden" include words such as heavy, dull, cumbersome, burdensome, ponderous, slow, plodding, laborious and tedious. These synonyms can be used interchangeably in sentences where the meaning of leaden is required. For instance, one could use the word "ponderous" instead of "leaden" when describing a slow and cumbersome object or task. On the other hand, one could use "tedious" to replace leaden when describing work that is slow and laborious. Ultimately, using the synonym that best fits the intended context will produce the desired effect.