Select the option that can be used as a one-word substitute for the given group of words.

Not fit to eat

Inedible

The term "inedible" refers to something that is not suitable or safe to be eaten. It indicates that the item or substance lacks the necessary qualities or characteristics to be consumed as food. In the given group of words, "not fit to eat," the word "inedible" precisely conveys the meaning of something that should not be consumed.

"Sullen" describes a person's mood or demeanor, typically characterized by gloominess or resentment. It does not relate to the concept of being unfit for consumption.

"Potable" refers to something that is safe and suitable for drinking. While it involves the idea of consumability, it specifically pertains to liquids that can be ingested, not to items that are not fit to eat.

"Fragile" refers to something that is delicate or easily broken or damaged. It does not convey the idea of being inedible.

Therefore, "Inedible" is the most appropriate one-word substitute for the given group of words as it specifically represents something that is not suitable or safe to be eaten.