David K. Barnhart (born 1941) is an American lexicographer who specializes in new words. He began his career helping his father, Clarence Barnhart, edit the Thorndike-Barnhart dictionary series.
In 1982 he, with his father, began work on The Barnhart Dictionary Companion, a quarterly publication documenting appearance of new words, new meanings and new usages in English. This carries on the tradition of the Barnhart Dictionary of New English series (edited by his father, brother Robert Barnhart, and Sol Steinmetz), which was last published in 1990. He wrote Neo Words: A Dictionary of the Newest and Most Unusual Words of Our Time (1991). He created The Barnhart New-Words Concordance (1994) and its Supplement (2006), an index to the words contained in numerous new word dictionaries, which has been updated several times.
With Allan A. Metcalf, he wrote America in So Many Words: Words that have shaped America (1997). He has worked as a teacher, lecturer, and as an expert witness reporting on usage and meaning in English.
He is a past president of the Dictionary Society of North America. He is a member of the American Dialect Society, the International Linguistic Association and the Modern Language Association.