Clarence Lewis Barnhart (1900-1993) was an American lexicographer best known for writing the Thorndike-Barnhart series of graded dictionaries , which were based on word lists developed by psychological theorist Edward Thorndike .

He created the American College Dictionary , published by Random House in 1947, which was later used as the basis of the Random House Dictionary. His three-volume New Century Cyclopedia of Names, published in 1954, was an expansion of the original 1894 volume of the Century Dictionary and Cyclopedia.

His largest general dictionary was the World Book Dictionary, a two-volume work created as a supplement to the World Book Encyclopedia. It was first published in 1963 and revised in 1976, totaling over 225,00 entries. Consistant with the encyclopedia's use by young people, he wrote definitions which were both simple and acurate, and most entries include sample sentences or phrases. Like Webster's Third New International, it included few proper names, leaving them to be covered by the encyclopedia.

He also co-edited the three editions of the Dictionary of New English , covering new words from the 1960s through the 1980s. His sons, David Barnhart and Robert Barnhart, are also lexicographers of note.