Definition - The following definition is from the OED:

"A book dealing with the individual words of a language (or certain specified classes of them), so as to set forth their orthography, pronunciation, signification, and use, their synonyms, derivation, and history, or at least some of these facts: for convenience of reference, the words are arranged in some stated order, now, in most languages, alphabetical; and in larger dictionaries the information given is illustrated by quotations from literature…."

1. For an analysis of the concept of looking something up in "The Dictionary," click HERE.

Example -
The Online Dictionary of Language Terminology (the ODLT)

Etymology -
The word derives from the Medieval Latin dictionarium, a collection of words and phrases, which in turn derives from the Latin dictio, word. The word was probably first used as part of the title of a book in Sir Thomas Elyot's Latin Dictionary (1538).

Oxford English Dictionary -
Its first citation is from 1526:
"And so Peter Bercharius in his dictionary describeth it.'
(Pilgr. Perf. (W. de W. 1531), 233)

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