Linguists say they have determined that a unique sign language, possibly dating back to the 1800s or before, is being used in Hawaii, marking the first time in 80 years a previously unknown language — spoken or signed — has been documented in the U.S.

Researchers will formally announce their findings this weekend showing it’s not a dialect of American Sign Language, as many long believed, but an unrelated language with unique vocabulary and grammar.

Only about 40 people, most in their 80s, are known to currently use Hawaii Sign Language, meaning the discovery comes just as the language is on the cusp of disappearing.

"I think that everyone in the room is aware of how Hawaiian, the indigenous language of this state, has been brought back from the brink of extinction," William O’Grady, linguistics professor at the University of Hawaii, said at a news conference. "But what we didn’t know until very recently is that Hawaii is home to a second highly endangered language that is found nowhere else in the world."

Researchers said they interviewed and videotaped 21 users of Hawaii Sign Language — 19 elderly deaf people and two adult children of deaf parents — for their study.

They documented how Hawaii and American sign languages have different grammar. In Hawaii Sign Language, adjectives come after nouns, like "dog black" instead of "black dog" in American Sign Language.

The found words for father, mother, dog and pig are all different in Hawaii and American sign languages. In fact, only 20 words on a list of 100 key words are significantly similar in both languages.

"It’s clearly a separate language and it clearly developed independently," said James Woodward, a University of Hawaii, Manoa linguistics adjunct professor and co-director of the Center for Sign Linguistics and Deaf Studies at the Chinese University of Hong Kong.

Languages are considered dialects when they share more than 80 percent of the words on the list, said Woodward who has documented distinct sign languages in Thailand, Vietnam and other parts of Asia.

Languages are considered related if between 36 to 80 percent of the words on the list are significantly similar.

Four scholars involved in the research plan to present their study at the 3rd International Conference on Language Documentation and Conservation in Honolulu on Sunday.

Academics became aware of Hawaii Sign Language’s unique characteristics because of Linda Lambrecht, an American Sign Language instructor at Kapiolani Community College in Honolulu.

She grew up learning Hawaii Sign Language from her brothers, and it was her first language.

But at school she was taught to use American Sign Language, which entered Hawaii in the 1940s and became the dominant sign language in the islands by the 1950s.

She held on to her first language regardless, and used both. Later in life, she began approaching other scholars about researching it.

The attention it’s now receiving helps her look past the lack of interest people paid to it before.

"It will be recognized in addition to the sign languages of other countries, and that itself makes me so proud that I don’t feel that frustrated," Lambrecht said through an interpreter.

O’Grady said Hawaii Sign Language is the first previously unknown language to be documented in the United States since the 1930s, when scholars identified the South Central Alaska spoken language of Eyak as unique.

Sign language was used in Hawaii in the 19th century, if not earlier. The first known written reference to sign language in the islands is in an 1821 letter from Protestant missionary Hiram Bingham to his friend Thomas Hopkins Gallaudet, said Barbara Earth, a University of Hawaii, Manoa adjunct assistant professor and Gallaudet University research fellow. Gallaudet co-founded one of the first deaf schools in the U.S.

Researchers plan to publish three Hawaii Sign Language textbooks and a dictionary to help keep the language alive. They also plan to publish their findings in academic journals