Which adjective means marked by a pretentious display or showiness?

The adjective that means marked by a pretentious display or showiness is "ostentatious." This term is commonly used to describe something that is overly elaborate or designed to attract attention or admiration, often in a way that is considered excessive or exaggerated. When someone is described as being ostentatious, it usually implies that they are trying to show off wealth, status, or achievements in a conspicuous manner.

In contrast, the other options do not convey the same meaning. "Affluent" refers to having a great deal of money or wealth, but it does not imply showiness; "paucity" indicates a lack or scarcity of something, which is unrelated to showiness; while "obtruded" means to impose oneself or one's ideas on others in an unwelcome way, and does not relate to the concept of display or showiness at all. Thus, "ostentatious" is the most fitting choice for describing something characterized by showy pretentiousness.