noun
A reference work listing words or names from one or more languages, usually ordered alphabetically, explaining each word's meanings or senses, oftentimes also containing information on its etymology, pronunciation, usage, semantic relations, translations, as well as other relevant information.
(by extension) A reference work on a particular subject or activity in which the entries are arranged alphabetically; an alphabetical encyclopedia.
(figurative) A person or thing regarded as a repository or compendium of information.
(with of or possessive, frequently figurative, especially derogatory) The collection of words used or understood by a particular person; vocabulary.
(preceded by the) A synchronic dictionary of a standardised language held to only contain words that are properly part of the language.
(computing) 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).
verb
(transitive) To look up in a dictionary.
(transitive) To add to a dictionary.
(intransitive, rare) To compile a dictionary.