There are few ways the word Horcrux could come out of Harry's mouth that I would not take as evidence for Harry doing outside research. It would take non-trivial circumlocutions to indicate that Harry doesn't know what the English word Horcrux means. Such circumlocutions appear in the text. The best reason I can think of for those circumlocutions to appear in the text is to prevent people like me from inferring too much from Harry's vocabulary choice. There are alternatives explanations, like hinting that Salazar invented Horcruxes, but they seem less likely to me.
It would take non-trivial circumlocutions to indicate that Harry doesn't know what the English word Horcrux means.
And what circumlocutions are those, exactly? Because in the passage quoted, I see a straightforward explanation of the ritual and a naming in English (with the unexpected result that he knew the English word's equivalent in Parseltongue too).
New chapter!
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 102.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: