Further, each word may have multiple meanings. Some dictionaries include each separate meaning in the order of most common usage while others list definitions in historical order, with the oldest usage first.

In many languages, words can appear in many different forms, but only the undeclined or unconjugated form appears as the headword in most dictionaries. Dictionaries are most commonly found in the form of a book, but some newer dictionaries, like StarDict and the New Oxford American Dictionary are dictionary software running on PDAs or computers. There are also many online dictionaries accessible via the Internet.

The oldest known dictionaries were Akkadian empire cuneiform tablets with bilingual Sumerian-Akkadian wordlists, discovered in Ebla (modern Syria) and dated roughly 2300 BCE. The early 2nd millennium BCE Urra=hubullu glossary is the canonical Babylonian version of such bilingual Sumerian wordlists. A Chinese dictionary, the ca. 3rd century BCE Erya, was the earliest surviving monolingual dictionary, although some sources cite the ca. 800 BCE Shizhoupian as a "dictionary", modern scholarship considers it a calligraphic compendium of Chinese characters from Zhou dynasty bronzes. Philitas of Cos (fl. 4th century BCE) wrote a pioneering vocabulary Disorderly Words (Ἄτακτοι γλῶσσαι, Átaktoi glôssai) which explained the meanings of rare Homeric and other literary words, words from local dialects, and technical terms. Apollonius the Sophist (fl. 1st century CE) wrote the oldest surviving Homeric lexicon. The first Sanskrit dictionary, the Amarakośa, was written by Amara Sinha ca. 4th century CE. Written in verse, it listed around 10,000 words. According to the Nihon Shoki, the first Japanese dictionary was the long-lost 682 CE Niina glossary of Chinese characters. The oldest existing Japanese dictionary, the ca. 835 CE Tenrei Banshō Meigi, was also a glossary of written Chinese.

Arabic dictionaries were compiled between the 8th and 14th centuries CE, organizing words in rhyme order (by the last syllable), by alphabetical order of the radicals, or according to the alphabetical order of the first letter (the system used in modern European language dictionaries). The modern system was mainly used in specialist dictionaries, such as those of terms from the Qur'an and hadith, while most general use dictionaries, such as the Lisan al-`Arab (13th c., still the best-known large-scale dictionary of Arabic) and al-Qamus al-Muhit (14th c.) listed words in the alphabetical order of the radicals. The Qamus al-Muhit is the first handy dictionary in Arabic, which includes only words and their definitions, eliminating the supporting examples used in such dictionaries as the Lisan and the Oxford English Dictionary.

The earliest modern European dictionaries were bilingual dictionaries. The earliest in the English language were glossaries of French, Italian or Latin words along with definitions of the foreign words in English. An early non-alphabetical list of 8000 English words was the Elementarie created by Richard Mulcaster in 1592.

The first purely English alphabetical dictionary was A Table Alphabeticall, written by English schoolteacher Robert Cawdrey in 1604. The only surviving copy is found at the Bodleian Library in Oxford. Yet this early effort, as well as the many imitators which followed it, was seen as unreliable and nowhere near definitive. Philip Stanhope, 4th Earl of Chesterfield was still lamenting in 1754, 150 years after Cawdrey's publication, that it is "a sort of disgrace to our nation, that hitherto we have had no… standard of our language; our dictionaries at present being more properly what our neighbors the Dutch and the Germans call theirs, word-books, than dictionaries in the superior sense of that title." It was not until Samuel Johnson's A Dictionary of the English Language (1755) that a truly noteworthy, reliable English Dictionary was deemed to have been produced, and the fact that today many people still mistakenly believe Johnson to have written the first English Dictionary is a testament to this legacy. By this stage, dictionaries had evolved to contain textual references for most words, and were arranged alphabetically, rather than by topic (a previously popular form of arrangement, which meant all animals would be grouped together, etc.). Johnson's masterwork could be judged as the first to bring all these elements together, creating the first 'modern' dictionary.

Johnson's Dictionary remained the English-language standard for over 150 years, until the Oxford University Press began writing and releasing the Oxford English Dictionary in short fascicles from 1884 onwards. It took nearly 50 years to finally complete the huge work, and they finally released the complete OED in twelve volumes in 1928. It remains the most comprehensive and trusted English language dictionary to this day, with revisions and updates added by a dedicated team every three months. One of the main contributors to this modern day dictionary was an ex-army surgeon, William Chester Minor, a convicted murderer who was confined to an asylum for the criminally insane.

In 1806, American Noah Webster published his first dictionary, A Compendious Dictionary of the English Language. In 1807 Webster began compiling an expanded and fully comprehensive dictionary, An American Dictionary of the English Language; it took twenty-seven years to complete. To evaluate the etymology of words, Webster learned twenty-six languages, including Old English (Anglo-Saxon), German, Greek, Latin, Italian, Spanish, French, Hebrew, Arabic, and Sanskrit. Webster hoped to standardize American speech, since Americans in different parts of the country used different languages. They also spelled, pronounced, and used English words differently.

Webster completed his dictionary during his year abroad in 1825 in Paris, France, and at the University of Cambridge. His book contained seventy thousand words, of which twelve thousand had never appeared in a published dictionary before. As a spelling reformer, Webster believed that English spelling rules were unnecessarily complex, so his dictionary introduced American English spellings, replacing "colour" with "color", substituting "wagon" for "waggon", and printing "center" instead of "centre". He also added American words, like "skunk" and "squash", that did not appear in British dictionaries. At the age of seventy, Webster published his dictionary in 1828; it sold 2500 copies. In 1840, the second edition was published in two volumes.

Austin (2005) explores the intersection of lexicographical and poetic practices in American literature, and attempts to map out a "lexical poetics" using Webster's dictionaries as the. He shows the ways in which American poetry has inherited Webster, has drawn upon his lexicography in order to reinvent it. Austin explicates key definitions from both the Compendious (1806) and American (1828) dictionaries, and brings into its discourse a range of concerns, including the politics of American English, the question of national identity and culture in the early moments of American independence, and the poetics of citation and of definition. Webster's dictionaries were a redefinition of Americanism within the context of an emergent and unstable American socio-political and cultural identity. Webster's identification of his project as a "federal language" shows his competing impulses towards regularity and innovation in historical terms. Perhaps the contradictions of Webster's project comprised part of a larger dialectical play between liberty and order within Revolutionary and post-Revolutionary political debates.