Which word would you use for something that is considered dull and heavy?

The term "ponderous" is used to describe something that is not only heavy in the literal sense but also connotes a sense of dullness or clumsiness in movement or effect. This word captures both the physical weight and the figurative sense of being slow or heavy in thought or presentation. For example, a ponderous piece of writing might be characterized by its laborious and tedious style, making it difficult for readers to engage with. The heaviness implied by "ponderous" suggests a lack of agility or lightness, which aligns well with the concept of dullness.

In contrast, the other terms do not correspond to the meaning of dullness and heaviness. "Pique" refers to arousing interest or curiosity, "penitent" describes a feeling of remorse or regret, and "pliant" suggests flexibility or adaptability, which are all unrelated concepts. Thus, "ponderous" is the most suitable choice for describing something that is both dull and heavy.