Look up Japanese words in Readest

Readest can hand the text you select to another app's dictionary. Turn that on once, and every sentence you select in a Japanese book opens in Fusen's popup, on top of the page, ready for you to tap the word you want.

Tested with Readest 0.12.16 and Fusen 1.0.1 on Android 16. Updated 26 October 2026.

Before you start

• Install Fusen and, when it asks, download the dictionary (JMdict, about 11 MB). After that, lookups work offline.
• Install Readest and open a Japanese EPUB in it.

Set up Readest once

Readest uses its own dictionaries until you tell it to use the phone's. You only do this once.

1. In a book, long-press a word, then tap the Dictionary icon (an open book with an A) in the menu that appears.

2. Readest opens its own dictionary sheet. Tap the gear at its top right. This opens Language › Dictionaries.

   You can also get there from Readest's settings: tap the middle of the page, tap A at the bottom, then More Settings, the Language tab and Manage Dictionaries.

3. Turn on System Dictionary. Readest turns Wiktionary and Wikipedia off at the same time.

   

Look up a word

1. Long-press the first character of the sentence. Readest selects a single character in Japanese, so drag the end handle to the end of the sentence (and the start handle back, if needed).

   

2. Tap the Dictionary icon. Android asks which app to use: choose Fusen (listed as Fusen lookup), then Just once, or Always to skip this question from now on.

   

3. Fusen's popup opens over the book with the sentence you selected. Tap any word in it to see its dictionary entry; conjugated verbs and adjectives are traced back to their dictionary form.

   Tap + beside a meaning to save the word to your notebook, with this sentence. Close the popup (× or Back) and you are back on the same page.

   

Vertical books (縦書き)

Readest lays out vertical Japanese books properly, and selecting works the same way: long-press, then drag the end handle down the column (and on to the next column to the left). Tap Dictionary as before.

Good to know

• Select the sentence, not just the word. Readest selects one character at a time, and Fusen saves whatever you sent as the word's sentence. Sending the whole sentence and tapping the word in the popup gives you both a correct lookup and a useful example.
• One collection per book. Tap the collection name at the top left of the popup (Inbox at first), choose New collection… and name it after the book. Words you save go there, and the popup stays on that collection until you change it.
• Furigana are left out. Ruby readings in the book are not part of the selection, so the popup shows the base text. Readings come from the dictionary instead.
• No Share in Readest's menu. If you prefer copying, the Copy icon works with Fusen's floating Lookup button: turn it on in Fusen with Settings → Behavior → Floating button, copy the text in Readest, then tap the button.
• Translate and explain. The popup's Translate translates the sentence, and Explain with AI explains the word in this context. Both use Fusen AI, with free monthly credits on a free Fusen account; the dictionary itself never uses credits.
• Dictionary opens Readest's own sheet instead of asking? System Dictionary is off. Turn it on as in Set up Readest once.