What is the DIC file format?
A .dic file is a dictionary file used by word processors and spell-checking tools as a word-list database for spelling correction. Dictionary files have long served as the backbone of spell checkers, and today the dominant standard is the Hunspell format - a plain-text file always paired with a same-named .aff affix rules file (for example, en_US.dic alongside en_US.aff).
In the Hunspell format, a .dic file opens with a line containing the approximate word count, followed by one stem word per line. Words can carry optional flag codes after a / character (e.g. walk/DGS), referencing prefix and suffix rules defined in the companion .aff file. The encoding is declared in .aff via the SET directive; UTF-8 is now standard, though older dictionaries still use ISO-8859 encodings. Hunspell dictionaries ship inside LibreOffice and Apache OpenOffice extensions (.oxt), Firefox and Chrome add-ons (.xpi), and are embedded in macOS and Android.
User dictionaries are a common variant - plain-text .dic files created by the user to store words not found in the main database. The main dictionary typically contains tens of thousands to hundreds of thousands of word stems, with files ranging from roughly 100 KB to 5 MB.
.dic files can also appear in software localization workflows, where source strings are sent to translators or stored as reference glossaries. Some dictionary files are distributed by dictionary software developers as integration aids for programmers building spell-check into their own applications.
Security & safety
RISK: LOWA .dic is a plain-text word list and contains no executable code, so the file itself is safe. The only realistic caution is the delivery wrapper: spell-check dictionaries are often installed as LibreOffice extensions (.oxt) or browser add-ons, and extensions can carry code - install language packs only from the official LibreOffice/AOO extension site or your browser's add-on store, not random download portals. The word-list file you can open and read in any text editor with no risk.
Format details
in a nutshell- Microsoft Office custom dictionary - CUSTOM.DIC - a plain-text user word list of terms added via 'Add to Dictionary' in Word/Office; one word per line, no affix file.
- CLEX / programming or CAD dictionary - Some applications (e.g. certain CAD, IDE or text tools) use .dic as a generic keyword/term list; structure is app-specific.
Programs that open DIC files
Windows3 apps
Microsoft Word
Paid For CUSTOM.DIC: File - Options - Proofing - Custom Dictionaries to add/manage. Word's custom dictionary is a plain word list. 
LibreOffice
Open-source Install the dictionary as an extension (Tools - Extension Manager - Add the .oxt), or place .dic + .aff in the user dictionary path. Then it's used automatically for spell check. 
Notepad / any text editor
Open-source Open the .dic as plain text to read or add words (one per line). For Hunspell, edit the count line and respect the .aff flags. 
macOS2 apps
LibreOffice
Open-source Add the dictionary via Extension Manager or the dictionary folder; macOS itself also uses Hunspell-style dictionaries system-wide. 
Microsoft Word for Mac
Paid Manage custom dictionaries under Word - Preferences - Spelling & Grammar - Dictionaries. 
Linux2 apps
LibreOffice
Open-source Drop en_XX.dic + en_XX.aff into the Hunspell dictionary directory (e.g. /usr/share/hunspell) or install via your package manager (hunspell-<lang>). 
Apache OpenOffice
Open-source Install the dictionary extension via Tools - Extension Manager. (Project is only sparsely maintained - LibreOffice is the active choice.)
Browser spell check (Firefox / Chrome)
Free Add a language dictionary through the browser's language settings / add-ons; it uses Hunspell .dic+.aff internally - no manual file handling needed. Technical details
deep spec| Format type | Plain-text word list; no binary signature or magic bytes |
| Companion file | Always paired with a same-named `.aff` affix rules file (e.g. `en_US.dic` + `en_US.aff`) |
| File structure | First line: word count integer; each following line: one word stem, optionally followed by `/flags` |
| Affix flag syntax | Flags appended after `/` on a stem line reference prefix/suffix rules in `.aff` (e.g. `walk/DGS`); flag format set by the FLAG directive in `.aff` |
| Character encoding | Declared in the paired `.aff` via the `SET` directive; UTF-8 for modern dictionaries; legacy files may use ISO-8859-x |
| MIME type | `text/plain`; informally `application/x-hunspell-dictionary` |
| Typical file size | 100 KB - 5 MB for full language dictionaries (tens of thousands to hundreds of thousands of word stems) |
| Distribution packaging | Bundled inside LibreOffice/OpenOffice `.oxt` extensions or Firefox/Chrome `.xpi` add-ons; installed in app-specific language folders |
| Platform support | Cross-platform: Windows, macOS, Linux, Android, and any application embedding the Hunspell library |
| Format lineage | Hunspell format (superset of MySpell, which extended Ispell); developed by László Németh in 2002, originally for Hungarian |
| User dictionary variant | Simplified `.dic` files containing only a plain word list (no affix flags), used by Microsoft Word to store user-added words |
| Reference spell-check engine | Hunspell; embedded in LibreOffice, Apache OpenOffice, Firefox, Chrome, and the macOS built-in spell checker |
| Language coverage | Over 100 language dictionaries available in Hunspell format, maintained by language communities and the LibreOffice project |
| Editability | Fully human-readable; can be opened and modified in any text editor - changes take effect after restarting the host application |
| Released | 2002 (Hunspell; building on MySpell/Ispell lineage from the 1980s-90s) |
| Latest version | N/A (no version on the .dic format; tracked per language dictionary release) |
| Open standard | Yes · royalty-free |
| Specification | manpages.ubuntu.com |
DIC conversions
Community Q&A
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