Dorothy Casterline, who as a young researcher at Gallaudet University in the early 1960s helped write the first comprehensive dictionary of American Sign Language, a book that revolutionized the study of Deaf culture, died on Aug. 8 in Irmo, S.C. She was 95.

Pamela Decker Wright, a professor at Gallaudet, the only university designed for the deaf or hard of hearing in the United States, said Mrs. Casterline died, in a hospital, from complications of a fall.

As an undergraduate English major at Gallaudet, in Washington, in the late 1950s, Mrs. Casterline, who had lost her hearing at 13, caught the attention of a professor named William Stokoe. In addition to teaching literature, Dr. Stokoe was investigating the grammar and syntax of sign language, which at the time was considered nothing more than a gestural derivative of spoken English.

Dr. Stokoe believed that there was much more to it. His goal, which he realized in 1965 with Mrs. Casterline and another professor, Carl Croneberg, as co-authors, was to compile the first systematic dictionary of what they came to call American Sign Language.

“The book was Bill’s idea, but Carl and Dorothy did most of the work,” Professor Wright said.

Dr. Stokoe had the vision, but he also had a problem: Not only was he hearing, but he had never studied sign language before arriving at Gallaudet in 1955.

Mrs. Casterline was one of his star students, who “wrote essays better than nine-tenths of the hearing students whose papers I had read for a dozen years elsewhere,” he wrote in the journal Sign Language Studies in 1993.

She was also something of an outsider, even among the deaf students at Gallaudet. Having been born in Hawaii to Japanese American parents, she was among the first students of color at the school — and, Professor Wright said, most likely the first person of color to join the faculty.

She graduated with honors in 1958. She then joined the English faculty as an instructor and worked as a researcher with Dr. Stokoe’s Linguistics Research Laboratory, alongside Mr. Croneberg, who was also deaf. (Dr. Stokoe died in 2000. Mr. Croneberg died in 2022.)

With a grant from the National Science Foundation, the trio filmed thousands of hours of interviews with people from all walks of life: children and college students, men and women, Northerners and Southerners.

It was the task of Mrs. Casterline, who had fine, precise handwriting, to transcribe the interviews and then use a specialized typewriter to compile and annotate them. She worked late into the night and on weekends, sometimes with her newborn son in one arm.

The result was a vast collection of signs, which, they argued in “A Dictionary of American Sign Language on Linguistic Principles” (1965), constituted not a variant of English but a language unto itself, with its own rules. The dictionary organized its entries by hand formations, not by the alphabetical order of their English equivalents.

It was not immediately welcome, either in the Deaf community or among linguists generally. The idea that sign language was merely a visual, gestural adjunct to spoken language was too ingrained.

“We’ve always had — and continue to still have — pictures to illustrate how a sign is made, so we’re conditioned to think of American Sign Language as a picture language,” Mrs. Casterline told Jane Maher, the author of “Seeing Language in Sign: The Work of William C. Stokoe” (1996). “Seeing these strange symbols for the first time can be daunting.”

But by the 1980s, the dictionary had become a cornerstone of a robust emerging cultural identity.

“I feel that if the book hadn’t been published,” Professor Wright said, “I am not sure where we would be now.”

Dorothy Chiyoko Sueoka was born in Honolulu on April 27, 1928. Her father, Toshie Sueoka, was a stonemason and ironworker, and her mother, Takiyo (Yanagikara) Sueoka, was a housemaid.

Dorothy, who was known as Dot, lost her hearing in seventh grade, though she never knew why. She completed high school at what is now the Hawaii School for the Deaf and Blind. While there, she successfully lobbied the Honolulu police to cease barring deaf residents from driving cars.

She spent three years after high school working to save money to attend Gallaudet; at the time, only students who lived in the 48 states could receive financial assistance. She enrolled in 1955 and graduated three years later.

She married James Casterline, who died in 2012. She is survived by three grandchildren. Her sons, Jonathan and Rex, died before her.

After working on the dictionary, Mrs. Casterline left Gallaudet to raise her family. She also worked for a company that added captions to classic movies.

Years later, she remained proud of her work with Dr. Stokoe and Mr. Croneberg.

She helped write the dictionary, she told Ms. Maher, “to show that deaf people can be studied as linguistic and cultural communities, and not only as unfortunate victims with similar physical and sensory pathologies.”