For your information, the Kids Open Dictionary is progressing. Recently, the dictionary achieved the milestone of having 10 percent of its word list defined. The definitions are submitted by people like you and me who are willing to contribute without expecting to be paid for our writing. The definitions need to be accurate, simple, and NOT COPIED from another source to ensure that they can be used without copyright issue.
You will be able to generate glossaries of terms for your student projects without any problems. The glossaries will be exactly what you want, no more, no less because you will pick the words. You will even be able to generate the glossary in a format that you can modify once you have downloaded it to your computer. This is perfect for those of you who create lessons that go beyond a textbook your school/district has purchased for you.
Join in. Write some definitions for the dictionary so that the job gets done sooner, and feel good that you have made a contribution to the open source community.