dictionary

dictionary · noun, verb¹

1. Proto-Indo-European*deyḱ-
2. Proto-Indo-European*déyḱeti
3. Proto-Italic*deikō
4. Latindīcō
5. Latindictiō
6. Latindictiōnārius?
7. Medieval Latindictiōnārium
8. Middle Englishdixionare
9. English todaydictionary

From Middle English dixionare, a learned borrowing from Medieval Latin dictiōnārium, from Latin dictiōnārius, from dictiō (“a speaking”), from dictus, perfect past participle of dīcō (“to speak”) + -ārium (“room, place”). By surface analysis, diction + -ary.

Dictionary · proper noun²

From dictionary.

First known use, by meaning

• from c. 1480 A reference work listing words or names from one or more languages, usually ordered alphabetically, explaining each term's meanings or senses, often also containing information on its etymology, pronunciation, usage, semantic relations, translations, as well as other relevant information.
• from c. 1480 A synchronic dictionary of a standardised language held to only contain words that are properly part of the language.
• from c. 1480 A reference work on a particular subject or activity in which the entries are arranged alphabetically; an alphabetical encyclopedia.
• from 1570s The collection of words used or understood by a particular individual.
• from 1730s Someone or something regarded as a repository or compendium of information.
• from 1950s An associative array; a data structure where each value is referenced by a particular key, analogous to words and definitions in a dictionary (noun sense 1).