This page covers eBook Dictionaries.
 The issues
Not everyone even sees the need of an eBook dictionary. They would not use one even if it was included. Often the definition of a word they don't know is simply inferred from the surrounding context or they just ignore it. Some even insist that they know all of the words anyway although that is seldom the case in practice.
Of course there are many different kinds of readers and eBooks that may have been written centuries ago when other words were being used more frequently that those today. In addition there are users reading works not written in their native language and may want a dictionary that contains meanings or better yet a dictionary that can translate the word to a different language.
For those that really want to look up a word there are some special problems that are encountered.
 Addressing the problem
There are two ways that a dictionary can be useful in an eBook. One way is to use it like a paper dictionary and just look up words. The second is to be able to select a word in the eBook you are reading and then look up that word as a popup while not leaving the eBook. Different eBook Readers support different features.
Many eBook readers do not support dictionaries in the manner outlined above. Of course a dictionary is a book and to that extent you could make an eBook out of it. The problem is that most people don't want to just read a dictionary from front to back. For this reason an eBook typically has a difference in the way it is built and even formatted to allow for direct lookup. This requires that the reading program be able to take advantage of this difference.
A dictionary eBook has special indexing to find the entries. A reader needs to have a method of accessing the words directly. If you are reading another book you may be able to select a word in that eBook and then access the dictionary using that selection. This is the major way that an eBook dictionary is used. The Cybook and the Kindle both use variations of this technique.
If the eBook Reader or program has a way to do keyboard style input of a word then the reader can support indexed lookup of the dictionary itself without needing to find the word in a book. Sometimes this is called dictionary searching but the words have to be in a special index for the search to avoiding finding some word that may appear in the definition.
It is possible to use a TOC capability and internal linking to access entries using some sort of cascading TOC with multiple selections. This works if the read supports internal linking but is awkward at best.
Thus the bottom line is that a dictionary has to be built differently from a regular book and the reader really needs a specialized facility to access the data.
Some readers only support one or just a few dictionaries while others allow multiples. Some will use a dictionary that you choose while others look up the word in every dictionary in your collection and display all the answers sequentially on a page.
Mobipocket and eReader are two formats that have specific dictionary support built into the format. However it is possible to use these dictionaries to support eBook reading programs reading books in other formats so long as the reading program itself has the support. DRM is supported by both formats.
Kindle has good dictionaries available for all their products.
LIT includes dictionary support and has a free dictionary that can be downloaded from the Microsoft web site.
There is an effort called Dictionary exchange format to consolidate all of the various free formats so that dictionaries can be shared. However, this does not address the dictionaries that have DRM. See: XDXF.
SDictionary is cross-platform dictionary project uses own open Sdict dictionary format. Currently it is known to work under UNIX, Win32 and Symbian OS.
 Translation Dictionaries
- XDXF format and StarDict - Lots of languages.
- Dizionario Dictionary Italiano Inglese PDF and Dizionario Dictionary Inglese Italiano in MobileRead eBook uploads
- StarDict free opensource dictionary
- Dict.org - A client/server implementation.
- Dict format is used by AlReader and others. It is available in Lingvo and Slovoed dictionaries - See Russian Forum for details
- A Digital Latin Dictionary: Latin dictionary for the Kindle.
 English Dictionaries
- Webster, Noah: Webster's Dictionary 1913 (with 110,875 words) in IMP (here), MOBI (here), EPUB (here) or RB (here) or DIC (here) from MobileRead eBook uploads
- XDXF dictionaries - XML Dictionary Exchange Format. Webster's Dictionary is here as well. Many dictionaries available.
- old source of a Random House Dictionary (with 19,300 words) from rhd.rb
- Encarta pocket dictionary (with 86,000 words) in LIT format from Microsoft
- MobileRead thread - adding a dictionary to a PRS500 or PRS505. Note this is look up only, not available when reading another book.
- StarDict free opensource dictionary
- MobiPocket sells dictionaries for their format
- eReader sells dictionaries for their format
- ABBYY Lingvo dictionaries for PC and mobile devices. See for online translation dictionaries.
- Dict ftp site - prepackaged and other dict files.
- WordNet by Princeton University in MOBI format
 French Dictionnaries
- Dictionnaire de l'Académie française de 1932-35 (8e édition) MOBI [(here)]
- Dictionnaire Littré (1860-1876) MOBI [(here)]
 eBook devices
The following devices can use a dictionary to look up words in an eBook you are reading:
- JetBook has built-in dictionary support with several dictionaries. Multi-Language translation as well.
- Kindle includes a dictionary and support in AZW (basically MOBI format). Only one dictionary can be used.
- Bookeen Cybook Gen3 include dictionary support for MOBI dictionaries. Multiple dictionaries will work.
- EBookwise-1150 includes a dictionary.
 Spelling dictionaries
While dictionaries for spelling checkers are really not dictionaries in the classic sense they are included for completeness.
- HunSpell - open source spell checker. The is the one used by Open Office.
- Micro spell - spell checker for Windows, useful with Sigil or other Book authoring software.
- How to Write a Spelling Corrector describes a 21 line Python program to check and correct for errors.
 For more information
- A MobileRead thread - covers how to make a MOBI dictionary in any language.
- A MobileRead thread - covers a dictionary for Cool Reader that runs on some Hanlin devices.
- http://www.idpf.org/epub/dict/ The idpf standard for Dictionaries and Glossaries in ePub 3