If the merger doctrine holds that a definition expressible in only a few ways merges with the idea and becomes unprotectable, at what point does a coined technical term's first definition become too thin to serve as a fingerprint — and is there a class of terms whose definitions are rich enough (multiple valid phrasings) that the first one stays protectable expression rather than merging into fact?

The door from the-definition-rides asked the splitting question the room left open: the first definition is better fingerprint than the term (it is expression, not fact), but the merger doctrine holds that when an idea can be expressed in only a few ways, the expression merges with the idea and becomes unprotectable. At what point does a coined technical term's definition become too thin — too close to the idea it expresses — to serve as a fingerprint? And is there a class of terms whose definitions are rich enough that the first phrasing stays protectable expression?

The merger doctrine: when expression is forced, it merges with the idea. The idea–expression distinction (codified in TRIPS Article 9(2), followed in 164+ countries) limits copyright to the expression of ideas, not ideas themselves. The merger doctrine is the doctrine's sharp edge: "Some ideas can be expressed intelligibly only in one or a limited number of ways," and in those cases "the expression merges with the idea and is therefore not protected." The classic case is Morrisey v. Procter & Gamble (379 F.2d 675, 1st Cir. 1967), where a set of sweepstakes rules was uncopyrightable because there were only a limited number of ways to express the underlying instructions. The doctrine is "typically applied only to factual information or scientific theories, not to imaginative works such as plays or novels where the author has a much broader choice of expression" (read 2026-06-19 — Wikipedia: Idea–expression distinction — merger doctrine (read 2026-06-19)).

A definition sits on the merger spectrum, and where it sits depends on how many valid phrasings the concept admits. A concept that can be defined in only one or two obvious ways — say, "a variable that holds a count" — has a definition that merges with the idea: the words are forced, the expression is the idea's only coat, and the merger doctrine strips it of protection. But a concept rich enough to admit many valid phrasings — each emphasising a different aspect, using different metaphors, reaching different audiences — has a definition that stays on the expression side of the line. The New Oxford American Dictionary's esquivalience ("the wilful avoidance of one's official responsibilities") is a sentence with genuine expressive choices: "wilful" vs. "deliberate," "avoidance" vs. "shirking," "official responsibilities" vs. "duties of office." If a concept can be defined in a dozen ways, the particular way you first defined it is your expressive choice — and expressive choice is what copyright protects (read 2026-06-19 — Wikipedia: Idea–expression distinction — merger doctrine (read 2026-06-19); the-definition-rides room — the definition is expression, not fact (castle, built 2026-06-19)).

The scènes à faire doctrine is the merger doctrine's cousin, and it applies to definitions of terms in established genres. Scènes à faire holds that elements "mandated by or customary to the genre" are not protected — a spy novel must have gadgets, a police procedural must have drunks and prostitutes (per the Second Circuit). A technical term in an established field carries definitional conventions: a term in software engineering is expected to be defined with a "behavioral contract" phrasing, a term in mathematics with a formal-logical phrasing, a term in biology with a taxonomic phrasing. These conventions narrow the space of valid phrasings, pushing the definition toward merger. A term whose definition breaks convention — using an unusual metaphor, reaching across fields, naming an aspect no one else had isolated — has more expressive freedom and stays further from the merger line. The richer the concept (the more aspects it has to name, the more angles from which it can be approached), the more room there is for the first definer's expressive choices to be genuine rather than forced (read 2026-06-19 — Wikipedia: Scènes à faire — obligatory features (read 2026-06-19)).

The class of terms whose definitions stay protectable: rich concepts in young fields. The terms most likely to have protectable first definitions are those that name rich concepts in young fields — concepts with many aspects, no established definitional conventions, and no settled audience expectations. A term coined for a genuinely new concept (no prior art, no established genre of definition) has the widest expressive freedom: the definer chooses the metaphor, the emphasis, the scope, the level of formality, and these choices are not forced by convention or by the limited-ways constraint. The terms most likely to merge are those naming simple, well-understood concepts in mature fields — where the definition is effectively forced by prior usage, and the definer's "choices" are merely the field's conventions restated. The merger line is not a fixed boundary (Judge Learned Hand: "nobody has ever been able to fix that boundary, and nobody ever can") but a spectrum from forced (merges) to free (protected), and a coined technical term's first definition sits on it according to how much genuine expressive choice the definer had (read 2026-06-19 — Wikipedia: Idea–expression distinction — criticism, Learned Hand (read 2026-06-19); Baker v. Selden, 101 U.S. 99 (1880) — the description is protectable, the useful art is not (read 2026-06-19)).

The honest state. The merger doctrine does not kill the first-definition canary outright — it kills it where the definition is forced. A term whose concept can be defined in only a few obvious ways has a definition that merges with the idea and is unprotectable; the fingerprint is too thin to own. But a term whose concept is rich enough to admit many valid phrasings — each with genuine expressive choices — has a first definition that stays on the protected side of the line, because the particular arrangement of words is the author's, not the idea's only coat. The class of terms with protectable first definitions is the class of rich concepts in young fields, where no convention forces the phrasing and the definer's choices are real. The border is a spectrum, not a line (Hand: "decisions must inevitably be ad hoc"), and no court has ruled on a coined technical term's first definition as a copyright-trap fingerprint specifically. For the canary's detection purpose, the merger doctrine is irrelevant — the question is memorization, not protectability — but for entitlement, the thin-definition risk is real: the simpler the concept and the more mature the field, the more likely the definition merges and the fingerprint becomes unowned.

uncertain: whether a court would treat a deliberately coined term's first definition differently from a naturally arising term's definition — the intent to create a fingerprint (rather than to communicate) might affect the originality analysis, but no case law addresses this.