Copyright does not Protect Names at All
Names and book titles and other short phrases are never protected by copyright, whether they are common or uncommon.
The US Copyright Office Circular 01 "Copyright Basics" states on page 2:
Copyright does not protect:
- Ideas, procedures, methods, systems, processes, concepts, principles, or discoveries
- Works that are not fixed in a tangible form (such as a choreographic work that has not been
notated or recorded or an improvisational speech that has not been written down)
- Titles, names, short phrases, and slogans
- Familiar symbols or designs
- Mere variations of typographic ornamentation, lettering, or coloring
- Mere listings of ingredients or contents
For more information, see Works Not Protected by Copyright (Circular 33)
Circular 33 "Works Not Protected
by Copyright" states on pGES 2-3:
Names, Titles, Short Phrases
Words and short phrases, such as names, titles, and slogans, are uncopyrightable because they contain an insufficient amount of authorship. The Office will not register individual words or brief combinations of words, even if the word or short phrase is novel, distinctive, or lends itself to a play on words.
Examples of names, titles, or short phrases that do not contain a sufficient amount of creativity to support a claim in copyright include:
- The name of an individual (including pseudonyms, pen names, or stage names)
- The title or subtitle of a work, such as a book, a song, or a pictorial, graphic, or sculptural work
- The name of a business or organization
- The name of a band or performing group
- The name of a product or service
- A domain name or URL
- The name of a character
- Catchwords or catchphrases
- Mottos, slogans, or other short expressions
Under certain circumstances, names, titles, or short phrases may be protectable under federal or state trademark laws. For information about trademark laws, visit the U.S. Patent and Trademark Office website or call 1-800-786-9199.
Use of a name from a previous work can be one element that makes the later work a derivative work, but the name of a character alone will not m make a later work derivative. There must be significant and distinctive aspects of the source work (not merely common or generic aspects, or bare ideas) that are sufficiently original to be protectable, and those must be used in the later work to make the later work derivative. Even then a fair use defense may apply.
Having giant spiders called 'aragogs' would probably not alone be enough to make a work derivative of a Harry Potter novel, but if the detailed description and behavior of those monsters was used, it might possibly do so.
Failure to object to an infringement does not forfeit copyright, and later infringements can still have legal action taken over them.
Distinctive Characters: Court Cases
The OP asks:
Are there any similar court cases?
In Nichols v. Universal Pictures Corporation, 45 F.2d 119 (2d Cir. 1930) the famous Judge Learned Hand wrote:
If Twelfth Night were copyrighted, it is quite possible that a second comer might so closely imitate Sir Toby Belch or Malvolio as to infringe, but it would not be enough that for one of his characters he cast a riotous knight who kept wassail to the discomfort of the household, or a vain and foppish steward who became amorous of his mistress. These would be no more than Shakespeare's "ideas" in the play, as little capable of monopoly as Einstein's Doctrine of Relativity, or Darwin's theory of the Origin of Species. It follows that the less developed the characters, the less they can be copyrighted; that is the penalty an author must bear for marking them too indistinctly.[Emphasis added]
In he later case of Anderson v. Stallone, 11 U.S.P.Q.2d 1161 (C.D. Cal. 1989) the court wrote:
The precise legal standard this Court should apply in determining when a character may be afforded copyright protection is fraught with uncertainty. The Second Circuit has followed Judge Learned Hand's opinion in Nichols v. Universal Pictures, 45 F.2d 119 (2d. Cir. 1930), cert. denied, 282 U.S. 902 (1931). Judge Hand set forth a test, simple in theory but elusive in application, to determine when a character should be granted copyright protection. Essentially, under this test, copyright protection is granted to a character if it is developed with enough specificity so as to constitute protectable expression. Id. at 121.
...
The Rocky characters are one of the most highly delineated group of characters in modern American cinema. The physical and emotional characteristics of Rocky Balboa and the other characters were set forth in tremendous detail in the three Rocky movies before Anderson appropriated the characters for his treatment. The interrelationships and development of Rocky, Adrian, Apollo Creed, Clubber Lang, and Paulie are central to all three movies. Rocky Balboa is such a highly delineated character that his name is the title of all four of the Rocky movies and his character has become identified with specific character traits ranging from his speaking mannerisms to his physical characteristics. This Court has no difficulty ruling as a matter of law that the Rocky characters are delineated so extensively that they are protected from bodily appropriation when taken as a group and transposed into a sequel by another author.
Names may be Protected as Trademarks
A name may be protected as a trademark. This means that no one else can use it to promote or label a product or service of a similar type without permission. Trademarks do not expire as long as they remain in use. But trademarks only protect against uses "in trade", that is uses that identify a product, or are used to advertise that product, or are used to imply endorsement, approval or sponsorship of a product. If a reasonable person could be confused as the the source of a product, or who endorsed it, then the use of the mark may be infringing.
Trademarks are also country-specific. What is a protected mark in country A may be quite unprotected in country B.
While trademarks do not expire if they remain in use, if a term becomes "generic" and loses the distinctive association with a specific brand or maker, then it may also lose protection as a trademark. At one time Xerox feared that its name would become a generic synonym for "photocopy" and that it would lose trademark protection. It undertook to discourage people from using the mark "xerox" in connection with photocopying using non-Xerox equipment. Similarly the maker feared that "Kleenex" would become a generic synonym for "face tissue" and took steps to avoid this. However, a single use would not cause this result, it would require widespread use amounting to a change in the language for such distinctive marks to lose protection.
I strongly suspect that "Harry Potter" has been protected as a trademark in a number of countries. I am far more doubtful that "aragogs" has been, or even could be, protected as a trademark. The word "aragogs" is one fictional element in the HP books, but it is not used to label, identify, or advertise those books (or related products). Thus it is probably not protected. And even if it were, using such a term in the text of a work of fiction is probably not infringing I could write a mystery novel in which one of my characters has a Coke without seeking permission, and it would not be infringing the soft drink company's trademark. Unless the "aragogs" appear in the title, blurbs, or advertising of the fan novel, or are in some other way used to identify or advertise the novel, they would not infringe on a prior trademark of JKR's even if she has obtained one.
