Which word best indicates something that is remarkably frightening or horrible?

The word "ghastly" is the best choice to indicate something that is remarkably frightening or horrible. It conveys a sense of extreme horror, shock, or disgust, often used to describe scenes or experiences that instill fear or revulsion. For example, one might use "ghastly" to describe a horrific accident or a terrifying nightmare.

In contrast, the other options do not align with this meaning. "Charming" suggests something delightful or enchanting, "beautiful" refers to aesthetic appeal, and "ordinary" indicates something commonplace or unremarkable. These terms evoke positive or neutral connotations, which do not capture the sense of dread or horror that "ghastly" conveys. Thus, "ghastly" stands out as the appropriate term for describing something that is both frightening and horrific.