Which term describes an abstraction of a character of an entity or substance?

The term that describes an abstraction of a character of an entity or substance is "attribute." In various contexts, attributes are specified properties or characteristics that define and describe a particular object or entity. They provide essential details that help in identifying and differentiating entities from one another.

While "designation," "characteristic," and "quality" do represent aspects of entities, they do not capture the broad and specific meaning associated with "attribute." Designation often refers to a name or title given to an entity rather than a descriptive property. Characteristic is a similar term but typically refers to a specific distinguishing feature rather than an abstract property. Quality usually relates to the standard of something's attributes but does not inherently convey the notion of an abstraction related to an entity or substance as effectively as attribute does. Thus, attribute is the most appropriate term in this context.