Quality, property, character, attribute, accident all denote one of the intelligible marks or indications by means of which a thing may be identified or its constitution be understood.
Quality is the term of widest application and may designate any such mark, material or immaterial, individual or generic.
A property is a quality that is proper to a species or type; it therefore belongs to a thing by virtue of that thing’s true or essential nature.
A character is a peculiar or distinctive quality more often of a class than of an individual. The term is used especially in scientific and philosophical writing with reference to the properties which distinguish an isolable subgroup (as a species) within a larger group (as a genus).
An attribute is a quality that is ascribed to a thing. The term may imply a lack of definite knowledge of the thing in question; thus, one can speak of the attributes of God, meaning the qualities men ascribe to him.
More often attribute denotes a quality that, though ascribed, is felt as an essential concomitant which must belong to a thing by reason of its nature.
An accident basically is a nonessential trait; in philosophical use, however, the term often means one of the qualities by which a thing manifests itself and implies, therefore, a contrast with the substance—or the real, but unapparent, nature—of the thing.
In more general use accident usually implies fortuitousness or lack of intrinsic value.