Kôjien (広辞苑), 5th Edition, Iwanami Press, 1998.
The Kôjien is the standard Japanese dictionary. It is quoted at the starting point of essays and sits on the desks of clerks at City Hall.
The entries include information on the classical forms of the verbs and the old kana spelling. Usually early quotations for each use of the word are given. There are illustrations for many entries.
In particular, it includes most standard, historical terms, many bibliographical names with real explanations, and a large selection of geographical names.
This dictionary is almost a necessity for anyone doing serious work in Japanese history or literature.