Which word describes something that is often hidden or intended to deceive?

The word that best describes something that is often hidden or intended to deceive is "ulterior." It refers to motives or intentions that are concealed or not immediately apparent, often suggesting that there is a hidden agenda behind someone's actions or words. This term is frequently used in contexts such as discussions about someone's true purposes or reasons for doing something, especially when those reasons may not be straightforward or honest.

In contrast, the other terms present different meanings: "underwhelming" denotes something that does not meet expectations or is lacking in impact, which does not relate to deception. "Obvious" refers to something that is easily perceived or understood, lacking any hidden quality. "Transparent," in a figurative sense, means open and clear, suggesting that there is no attempt to hide anything; therefore, it stands in direct opposition to the idea of something being deceitful or hidden.