What term describes something that is slow and clumsy due to great weight?

The term that accurately captures the idea of being slow and clumsy due to great weight is "ponderous." This word specifically describes something that is heavy or weighty, which leads to an unwieldy or cumbersome nature. It suggests a lack of grace or fluidity, often associated with physical objects or even metaphorically applied to ideas or writing that are heavy and difficult to engage with.

In contrast, other terms in the choices do not convey this meaning. "Zest" refers to great enthusiasm or energy, "gratifying" describes something that provides satisfaction or pleasure, and "amalgamate" means to combine or merge different elements into one. None of these terms relates to the description of slowness or clumsiness due to weight, making "ponderous" the most fitting choice in this context.