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Dictionary

Look up words while reading an EPUB using an offline StarDict dictionary stored on the SD card.

Supported Format

The reader supports StarDict dictionaries. When searching for dictionaries online, look for "StarDict format" or files with .dict, .idx, and .ifo extensions.

A dictionary folder must contain:

  • .idx — word index (required, must be uncompressed — a .idx.gz will not work; decompress it on your computer with gzip -d first)
  • .dict or .dict.dz — definition data (.dict.dz is supported as-is; entries are decompressed on the fly during lookup)
  • .ifo — metadata (optional)

Not supported: .syn synonym files (ignored), dictionaries with 64-bit index offsets (idxoffsetbits=64 in the .ifo — rare, and rejected with an error), and HTML-formatted definitions render as raw markup rather than styled text.

Setting Up a Dictionary

  1. Copy your dictionary folder(s) to /dictionaries/ on the SD card — one dictionary per folder, e.g. /dictionaries/webster/webster.idx + webster.dict.dz. A hidden /.dictionaries/ folder (dot-prefixed) works the same way, for keeping it out of the file browser.
  2. Open Settings → Reader → Dictionary on the device.
  3. Select a dictionary from the list, or None to disable lookups.

The Dictionary setting only appears when at least one usable dictionary folder exists. Folders containing more than one dictionary (multiple .idx stems) are skipped as ambiguous.

Looking Up a Word

Two ways to start a lookup while reading:

  • Open the reader menu (Confirm) and choose Look Up.
  • Or set Settings → Controls → Long-press Menu to "Dictionary", then hold Confirm (~0.4s) on the reading page.

One word on the page becomes highlighted:

  1. Use Left/Right to move between words in reading order, and the side Up/Down buttons to jump between lines.
  2. Press Confirm to look up the highlighted word.
  3. Press Back to return to the reader.

On the very first lookup with a dictionary (and again if the dictionary file changes), the reader shows "Indexing dictionary…" while it builds a small .qidx sidecar file next to the .idx. This takes a few seconds for large dictionaries and makes all subsequent lookups fast. The sidecar can be deleted safely at any time — it will simply be rebuilt.

How Lookup Works

  1. Direct match — the word is found as-is (case-insensitive) in the dictionary index. Surrounding punctuation is ignored.
  2. Stemming — on a miss, common English word forms are retried automatically: possessives and plurals (dogs → dog, stories → story) and verb endings (walked → walk, running → run, making → make).
  3. Not found — a short popup appears and you return to word selection.

The Definition Screen

When a word is found, the definition screen shows the matched headword at the top and the definition text below, with a page counter for long definitions.

  • Left/Right or side Up/Down — previous / next page
  • Back — return to word selection

Where to find dictionaries

credit to https://github.com/koreader/koreader/wiki/Dictionary-support for the list.