cursor-dictionary.nvim

A Neovim plugin that displays dictionary translations for the word under the cursor in a split window.

Demo

cursor-dictionary-demo.mp4

Features

• Looks up the word under the cursor and shows its translation in a bottom split window
• Supports CSV and EIJIRO dictionary formats (converted to .cdict binary format)
• Toggle on/off with a single command

Installation

Using lazy.nvim:

{
  "whtsht/cursor-dictionary.nvim",
  config = function()
    require("cursor-dictionary").setup({})
  end,
}

A bundled English-Japanese dictionary (default-dict.cdict, ~46,000 entries) is used automatically when no dict is configured. Source: EJDict.

To use EIJIRO instead:

return {
  "whtsht/cursor-dictionary.nvim",
  config = function()
    require("cursor-dictionary").setup({
      dict = {
        source = vim.fn.expand("~/Downloads/EIJIRO-1448.TXT"),
        dir = vim.fn.expand("~/.local/share/nvim/cursor-dictionary/"),
        format = "eijiro",
      },
      enabled = false,
    })
  end,
}

On first startup, the source file is automatically converted to .cdict and saved to <dir>/dict.cdict. Subsequent startups skip the build and load the cached file directly.

Dictionary Setup

Supported formats

CSV — two-column format:

hello,こんにちは
world,世界
function,関数

EIJIRO — set format = "eijiro" and point source at the .TXT file (CP932 encoding). Requires iconv to be available on $PATH.

Configuration

require("cursor-dictionary").setup({
  -- omit `dict` to use the bundled default dictionary
  dict = {
    source = "/path/to/source",  -- path to CSV or EIJIRO .TXT file
    dir    = "/path/to/dir",     -- output directory; dict.cdict is saved here
    format = "csv",              -- "csv" or "eijiro"
  },
  enabled = false,  -- start disabled (default: false)
})

Commands

Command	Description
:CursorDictToggle	Toggle the dictionary window on/off

.cdict Format

.cdict is a custom binary format for fast, low-memory lookups. All integers are little-endian.

Header (24 bytes):
  magic[8]:           "CDICT\x01\x00\x00"
  entry_count[4]:     uint32
  key_index_start[4]: uint32  (absolute offset)
  key_pool_start[4]:  uint32  (absolute offset)
  val_pool_start[4]:  uint32  (absolute offset)

Key Index (entry_count × 12 bytes, sorted lexicographically):
  key_offset[4]: uint32  (offset into key pool)
  key_len[2]:    uint16
  val_offset[4]: uint32  (offset into val pool)
  val_len[2]:    uint16

Key Pool: concatenated lowercase key strings
Val Pool: concatenated translation strings (newline-separated when multiple definitions)

At startup, the Key Index and Key Pool are loaded into memory. The Val Pool is accessed on-demand via file seek. Lookup uses binary search entirely in memory; only the matched translation requires a file read.

Acknowledgements

Inspired by mouse-dictionary, a browser extension that displays dictionary definitions for words under the mouse cursor. This plugin brings the same concept to Neovim.