A reference guide to the imaginary world of Harry Potter says one of the magic spells in the books is based on the Hawaiian word aloha.

However, J.K. Rowling, author of the popular fantasy series, testified in a lawsuit that the made-up word is based on an African language.

Steven Vander Ark, 50, was called to the stand today in Manhattan federal court by a lawyer for Rowling and Warner Bros. Entertainment. They claim that his reference book, "Harry Potter Lexicon," infringed Rowling's copyrights on her seven best-selling books.

Rowling sat quietly as Vander Ark testified about "Lexicon" entries describing words and characters, such as "acromantula" — a large spider — that she created. David Hammer, the lawyer for his publisher, RDR Books, told Vander Ark that Rowling said the "Lexicon" gives the wrong etymology for some words.

The "Lexicon" says "Alohomora," a magic spell that causes objects to fly, stems from the Hawaiian word "Aloha." Rowling testified yesterday it came from a West African dialect.

"Oh, really!" Vander Ark said, after Hammer told him of Rowling's testimony. "This is exciting stuff for me."

At one point, Vander Ark broke down in tears when asked if he still felt part of the Harry Potter fan community following the lawsuit to block his work.

"I did," Vander Ark began, then adding, "I do." Wiping tears and turning from Rowling's gaze, he said the suit and resulting controversy have proven "difficult" for him. "This has been an important part of my life for nine years or so, and to have it turn into —" he testified, unable to complete his sentence. "It was never my intention."

The "Lexicon" lists alphabetically the characters, places, spells, creatures and objects in the Potter books. The key issue in the non-jury trial is whether Vander Ark made "fair use" of Rowling's work, as the defense claims. Federal law allows others to use copyrighted work for research, criticism and commentary.

Rowling testified yesterday that much of the "Lexicon" is stolen from her seven books and two research guides. She said plagiarists will flood the market with "Harry Potter" books unless a judge blocks publication of the "Lexicon," which may sell for $24.95. She has said that she plans to publish her own Potter encyclopedia and give the proceeds to charity.

The Potter books have sold more than 375 million copies worldwide. Warner Bros. sued RDR in October, seeking to block the release of the "Lexicon." Vander Ark also operates a free Harry Potter Web site that Rowling isn't challenging.

The seventh and final book about the fictional boy wizard, "Harry Potter and the Deathly Hallows," broke publishing records by selling 8.3 million copies in the U.S. in its first 24 hours in July and 11.5 million copies in its first 10 days. In the U.S., the books are published by Scholastic Corp., which isn't involved in the case.

Five films based on the books have grossed more than $4 billion, according to Warner Bros., a unit of New York-based Time Warner Inc., the world's largest media company.

"A fan's affectionate enthusiasm should not obscure acts of plagiarism," Rowling and Warner Bros. said in a statement after Vander Ark's testimony. "The problem remains that the Lexicon takes an enormous amount of Ms. Rowling's work and adds virtually no original commentary of its own."

Vander Ark, the main author of the "Lexicon," insisted he'd done nothing wrong in compiling his guide. "The 'Lexicon' is a reference book to a piece of literature," he testified.

Vander Ark, then a Michigan middle school librarian, said he read the first "Harry Potter" book in 1998 and launched his Web site in 2000. By 2007, the site had a small unpaid staff, had grown to 800 pages, and had won an award from Rowling. It earned about $1,000 a year selling ads.

Vander Ark said he initially believed that a book would violate Rowling's copyright. In August, Vander Ark changed his opinion after RDR owner Roger Rapoport approached him and said a dictionary would be lawful. Rowling's seventh book had been published weeks earlier.

"It collects the facts in a way that makes them easy to access," said Vander Ark, who now lives in London.

He cited a section on what he called "medical magic," which he said were "various spells and things." He said, "This is the kind of thing we put together as reference librarians."

Vander Ark was confronted by Rowling's lawyers with language that appeared taken from the Potter books. To describe memories leaking from a brain, she wrote they were like "ribbons of moving images" that were "unraveling like rolls of film." Vander Ark used almost identical words in his book.

"We use similar descriptions," he said.

Vander Ark acknowledged that he's accused others of plagiarizing his Web site and that he sued Warner Bros. for using what he said was his Potter timeline on a DVD the studio released. "No one has the right to use my work," Vander Ark wrote on his site.

Rowling's lawyer, Dale Cendali, played a clip of Vander Ark speaking at a Potter convention last year. "Jo has quit," Vander Ark says on the clip, referring to Rowling, whose first name is Joanne. "We're taking over." Today, he denied that he thought fans had the right to determine the fate of Rowling's characters.