Which of the following words means extremely bad or of low quality?

The word "abysmal" is commonly understood to mean extremely bad or of very low quality. It often conveys a sense of depth or severity in its negative connotations, making it suitable to describe situations, conditions, or performances that are profoundly unsatisfactory or disappointing.

In contrast, the other words provided have different meanings that do not align with the idea of being of low quality. "Agog" refers to being very eager or excited to hear or see something; "ameliorate" means to make something better or improve it; and "acolyte" denotes a person who assists in religious services, or, more broadly, someone who follows or assists a leader or authority figure. These definitions highlight why "abysmal" is the only word that directly fits the description of being extremely bad or of low quality.