Origins
The English word 'dictionary' comes from Medieval Latin 'dictiōnārium,' a word coined to describe a collection of 'dictiōnēs' — words or expressions. Latin 'dictiō' means 'a saying' or 'a word,' derived from 'dictus,' the past participle of 'dīcere' (to say, speak, tell). The PIE root behind 'dīcere' is *deyḱ- (to point, show), which links 'dictionary' to an ancient family of words rooted in the act of pointing things out.
The term 'dictionarius' first appears in a manuscript by John of Garland, an English grammarian working in Paris around 1225. His 'Dictionarius' was not a dictionary in the modern sense but a topically arranged word list designed to help students learn Latin vocabulary. The suffix '-ārium' (a place or collection for something, as in 'aquarium' or 'library' from 'librārium') marks it as a repository of words.
The first work in English actually titled 'Dictionary' was Sir Thomas Elyot's Latin-English reference published in 1538. Before this, English word lists were called 'vocabularies,' 'glossaries,' or 'word books.' The adoption of the Latinate term 'dictionary' reflected the humanist reverence for classical learning that characterized the Renaissance.
Development
The great landmarks of English lexicography followed. Robert Cawdrey's 'Table Alphabeticall' (1604) is often cited as the first monolingual English dictionary, though it covered only 'hard words' borrowed from other languages. Nathan Bailey's 'Universal Etymological English Dictionary' (1721) was the first to attempt comprehensive coverage. But the towering achievement of early English lexicography was Samuel Johnson's 'A Dictionary of the English Language' (1755), which combined rigorous definitions with illustrative quotations from literature. Johnson's work set the standard for over a century.
The 'Oxford English Dictionary,' begun in 1857 and first published in full in 1928, took the historical approach further, tracing each word's development through dated quotations. Noah Webster's 'American Dictionary of the English Language' (1828) established distinct American spelling conventions and asserted linguistic independence from Britain.
The Latin root 'dīcere' has been enormously productive in English. 'Diction' (manner of speaking), 'dictate' (to speak for another to write), 'dictator' (one who speaks commands), 'predict' (to say before), 'verdict' (truly said), 'contradict' (to speak against), 'edict' (something spoken out), 'benediction' (a good saying, a blessing), and 'malediction' (an evil saying, a curse) all descend from it. The connection to *deyḱ- (to point) also links it to 'indicate' (to point to), 'index' (the pointer), and 'digit' (the finger that points).
Latin Roots
Across the Romance languages, cognates are transparent: French 'dictionnaire,' Spanish 'diccionario,' Italian 'dizionario,' Portuguese 'dicionário.' Each language coined its term from the same Medieval Latin source, and each underwent the same semantic journey from 'a collection of sayings' to 'a reference book defining words.' The universality of this form across European languages testifies to the shared Latin intellectual culture from which modern lexicography emerged.