What term signifies a sudden and steep decline?

The term that signifies a sudden and steep decline is "plummet." In various contexts, this word is used to describe a rapid drop or fall, often with an implication of gravity or severity. For example, in finance, a stock price may plummet, indicating a significant and quick decrease in value. This term vividly evokes the idea of something dropping sharply, which is why it is the most suitable choice for describing such a steep decline.

On the other hand, the other options do not convey this meaning. "Pleasant" refers to something enjoyable or agreeable, "plea" pertains to a request or appeal, and "pompous" describes someone who is overly self-important. None of these terms relate to the concept of a rapid decline, reinforcing why "plummet" is the correct answer.