Look up Japanese words in Moon+ Reader

Moon+ Reader's Dict. button calls a ColorDict-style dictionary app by default, and Fusen answers that call. Select a sentence in a Japanese book, tap Dict., and Fusen's popup opens on top of the page, ready for you to tap the word you want.

Tested with Moon+ Reader 10.8 (free) and Fusen 1.0.1 on Android 15. Updated 27 October 2026.

Before you start

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

Moon+ Reader needs no setup beyond one OK the first time you tap Dict.

Look up a word

Long-press the first word of the sentence. Moon+ selects a short phrase and shows Copy · Highlight · Note · Dict. · More; drag the end handle to the end of the sentence.
Tap Dict. The first time, Customize dictionary opens with Dict.1 (Single-tap on Dictionary button) set to ColorDict/BlueDict/GoldenDict. Leave it as it is and tap OK at the bottom.

Fusen answers that ColorDict request. If another ColorDict-style dictionary app is installed too, Android asks which app to use: tap Fusen lookup.
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. From now on, Dict. opens Fusen straight away.

More lists every app that takes selected text, and Fusen lookup (Fusen) is one of them. It works with no setup, whatever Dict. is set to.

Moon+ Reader's More menu over a selected sentence: Share, Search, Read aloud, Fusen lookup (Fusen), Customize.

More → Share → Fusen lookup works too, and so does Copy with Fusen's floating Lookup button (turn it on in Fusen with Settings → Behavior → Floating button).

Vertical books (縦書き)

Moon+ Reader 10.8 shows vertical Japanese books horizontally: the text runs left to right, and its Visual Options have no setting for vertical text. Looking up words works exactly as above. To read 縦書き as it was laid out, use ReadEra, Readest or Librera: all three display and select vertical text and work with Fusen.

Good to know

Select the sentence, not just the word. 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.
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.
Dict. opens another app? Use More → Fusen lookup (Fusen) instead: it works whatever Dict. is set to.
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.
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.