How to Say "Encyclopedia" in Japanese

百科事典

hyakkajiten[ça̠k̚ka̠ d͡ʑitẽ̞ɴ]

To say encyclopedia in Japanese, use 百科事典 (hyakkajiten). If unsure, use 百科事典. Wiktionary also lists 百科全書 (hyakkazensho).

Meaning: comprehensive reference work with articles on a range of topics (noun)

Ways to say it

“encyclopedia” in Japanese
Japanese	Romanization (Wiktionary)	IPA
百科事典	hyakkajiten	[ça̠k̚ka̠ d͡ʑitẽ̞ɴ] (narrow)
百科全書	hyakkazensho	[ça̠k̚ka̠zẽ̞ɰ̃ɕo̞] (narrow)

百科事典 is the usual word for a reference work with articles on a wide range of subjects.

百科事典 combines 百 (hundred), 科 (subject) and 事典 (reference book).

百科事典 is the common modern term. 百科全書 (hyakkazensho) means the same but sounds more formal or literary. The loanword エンサイクロペディア also exists.

It is romanized hyakkajiten.

The term 百科全書 is a direct translation of the French 'Encyclopédie'. It was adopted into Japanese during the Meiji era as Japan sought to modernize its intellectual framework by importing Western concepts.
In Japanese, there is a distinction between 事典 ('dictionary of facts') and 辞典 ('dictionary of words'). While both can be translated as 'dictionary', the former is specifically for encyclopedic knowledge, while the latter is for language and definitions.
The number 百 (hyaku/hundred) in both terms is often used idiomatically to mean 'all' or 'every', rather than a literal count of one hundred.

その百科事典の改訂版が出版された。
A revised edition of the encyclopedia was published.
百科事典 here is the encyclopedia that got a revised edition.
Tatoeba #207080 by KK_kaku_, translation #44330 by CM
来月、その百科事典の最新版がでる。
An up-to-date edition of the encyclopedia will come out next month.
This sentence talks about the newest edition of 百科事典 coming out next month.
Tatoeba #78695 by mookeee, translation #325021 by CK
私は大学で百科事典を使用しています。
I use an encyclopedia at university.
彼は最新の百科事典を執筆しました。
He wrote the latest encyclopedia.
この事典は情報が豊富です。
This dictionary has abundant information.
古い百科事典を整理した。
Furui hyakajiten o seiri shita.
I organized some old encyclopedias.

A library setting where two students are studying.

陽太 Yota

この百科事典を借りてもいい？
Kono hyakajiten o karitemo ii?
Can I borrow this encyclopedia?
美咲 Misaki

いいよ、でも注意して使ってね。
Ii yo, demo chuui shite tsukatte ne.
Sure, but please be careful with it.
陽太 Yota

分かった、ありがとう。
Wakatta, arigatou.
Got it, thanks.
美咲 Misaki

どういたしまして。
Douitashimashite.
You're welcome.

Sources

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