William Dwight Whitney (1827-1894) was an American linguist, philologist, and lexicographer who edited The Century Dictionary.

Born in Northampton, Massachusetts, February 9, 1827. He entered Williams College at fifteen, graduating in 1845. He continued studying and worked at a bank in Northampton for several years, then assisted his brother Josiah Whitney on a geological survey of the Lake Superior region in 1849. For three years, he studied Sanskrit in Germany, and gained wide reputation for his scholarship in the field. At Yale, he became professor of Sanskrit in 1854, adding comparative philology in 1869. He also taught modern languages at the Sheffield Scientific School. He served as secretary to the American Oriental Society from 1857 until he became its president in 1884.

Whitney revised definitions for the 1864 edition of Webster's American Dictionary, and in 1869 became a founder and first president of the American Philological Association. He wrote metrical translations of the Vedas, and numerous papers on the Vedas and linguistics, many of which were collected in the Oriental and Linguistic Studies series (1872-74). He wrote several books on language, and grammar textbooks of English, French, German, and Sanskrit.

In his Course in General Linguistics in the chapter on the 'Immutability and Mutability of the Sign', Ferdinand de Saussure credits Whitney with insisting on the arbitrary nature of the linguistic signs.

Although he suffered from a heart ailment in his later years, he was editor-in-chief of the first edition of the respected Century Dictionary, which appeared from 1889 to 1891. He was the brother of Professor Josiah Whitney. He married the daughter of US Senator & Governor of the State of Connecticut Roger Sherman Baldwin, Elizabeth Wooster Baldwin. His son was Assistant US Attorney General Edward Baldwin Whitney and his grandson was the much celebrated mathematician Hassler Whitney.