American lexicographer whose dictionaries rivaled those of Noah Webster (Webster, Noah) in popularity and critical esteem from about 1830 to 1865. His introduction of synonyms to definitions, as well as other innovations, was assimilated by later lexicographers.

Beginning in 1817 Worcester wrote several works that were widely used as textbooks, including A Gazetteer of the United States (1818) and Elements of History, Ancient and Modern (1826). From about 1828 until his death, however, he devoted himself almost entirely to lexicography. His abridgment of Webster's large American Dictionary of the English Language in 1829 was followed by his own Comprehensive Pronouncing and Explanatory Dictionary of the English Language (1830), which introduced the “compromise vowel” in such words as half, past, and dance, a sound intermediate between the a in “cat” and the a in “father.” The later work also elicited a charge of plagiarism from Webster and thus began a bitter publishing battle known as the “Dictionary War,” which lasted until Worcester's death.

His Universal and Critical Dictionary of the English Language (1846) was followed by enlarged editions of the 1830 Comprehensive. Most notable among them was the 1855 edition with the new title A Pronouncing, Explanatory, and Synonymous Dictionary of the English Language. In addition to its pioneering introduction of synonymy, it also included, for the first time in an English dictionary, given names and their etymological derivations. Worcester's largest and most successful work was the illustrated quarto Dictionary of the English Language (1860).

In the second half of the 19th century Worcester's dictionaries gradually lost out in competition with those of Webster, and they eventually ceased to be published. This was due largely to the more enterprising promotional and editorial policies undertaken by the publisher of the Webster dictionaries.