Proprietary eponyms are another matter entirely. These are general words that are, or were at one time, proprietary brand names or service marks. Kleenex, for example, is a brand of facial tissues, yet the word is used today to refer to facial tissues of any brand. Xerox is a brand of photocopy machine; that word, too, has been since adopted to refer to any brand of photocopy machine and, moreover, also employed as a verb to describe the act of photocopying. As this illustrates, although brand names are proper adjectives (as in, "Kleenex facial tissues"), when such terms are adopted for general use they tend to become nouns and often also verbs.