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I am developing a mobile word game in which the word list and word definitions come from the GCIDE Dictionary. According to my research this software is released under the GNU General Public License.

I am not using the dictionary's software, only the words and definitions that the software uses, which are originally compiled from other dictionaries (1913 Webster, WordNet, etc). I downloaded the word list separate from the application and copied it to my own formatted file.

My research on the license has led to a lot of concern with this:

Is this considered using/distributing the licensed dictionary software?

Am I able to sell my mobile game without releasing the source code to the public?

If I sell my mobile game, are purchasers able to redistribute my software freely since the dictionary is under a free license?

I want to avoid any future problems with this, so any suggestions are appreciated.

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The GCIDE dictionary itself is licensed under GPL-3.0. It consists of a bunch of files with markup, no software involved. Indeed, the GPL can also be applied to non-software works, though it is unusual.

When you use material under some license, you must comply with the terms of the license. In case of the GPL, there are two highly relevant conditions:

  • Everyone who receives a copy of the covered work (original or modified, in whole or in part) must receive the complete corresponding source code of the work, under the terms of the GPL-3.0.

  • If you create a derivative work of the covered work, the derivative work can only be distributed under the GPL-3.0.

However, selling the covered material is perfectly fine. The GPL does not forbid you to make money, however you must not profit from your requirement to provide the corresponding source code.

Here, the core question is whether your mobile game would be a derivative work of the GPL-licensed dictionary. If your game merely loads the dictionary as a data file, I don't think they would form a single derived work. However, if you compile the dictionary into your app, this would be more difficult to argue.

Ultimately, what is a derivative work will depend on a court. It could therefore be helpful to keep your app as clearly non-derivative as possible. I would avoid baking the dictionary into the app's binary but store it separately as a data file, would show attribution notices in reasonable places (e.g. a screen with attribution notices and the complete license text), and would make it possible for users to export a copy of the dictionary files. Furthermore, the GPL-3.0 may require you to allow users to modify this file, for example by making it possible to import a modified dictionary into your app.

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  • Thank you for the thorough response! This helps a lot.
    – Drew K
    Mar 2, 2021 at 19:37
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    Minor issue: "must receive the complete corresponding source code of the work" is not quite correct. They must receive the source code or an offer to give it to them.
    – Ryan M
    Mar 2, 2021 at 20:06
  • The GPL permits aggregation, so as long as you read the dictionary file at run time there shouldn't be a problem.
    – Paul Johnson
    Mar 2, 2021 at 21:26
  • Thanks Paul, this really eases my concern. I will be using the dictionary as a separate data file and read it to memory at run time to avoid it being part of my build. You all are life savers.
    – Drew K
    Mar 2, 2021 at 23:27
  • @DrewK I do not believe that is a valid legal test, actually - I believe amon is wrong here. The dictionary is still part of your app, no?
    – user253751
    Mar 4, 2021 at 12:52
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If you try to sell the software on Apples App Store you run into a problem: Apples terms and conditions state that any payment made by the customer is not for the software itself, but for the license to use it. But the GPL license states you are not allowed to charge for the license, only for the software. Together, these two terms mean that GPL licensed software on the App Store must be free of any charge.

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    According to the FSF, this is incorrect. Their position is that you cannot even distribute GPL software for free on the App Store. Also, this answer potentially misstates the reasoning: the issue is the imposition of additional restrictions on the licensee.
    – Ryan M
    Mar 3, 2021 at 6:51

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