Short answer: No.
I have been dealing with copyright issues for 30 years and in no respect are you able to copy definitions from any dictionary into a database for your use with the exception of fair use which does allow for referencing or quoting others work in your own work only if and when you are adding value to that work.
If you chose to use a part of a work for your work, that is fine if you reference the original work. You would be permitted to take a small portion of the definitions if you can reference them in some way. This would be appropriate for a paper you are writing for school or work, as an example. If the database is to be used by others, then it would be illegal to wholesale import their work into a database. However, if only some definitions are needed, then a footnote or link would be appropriate. You would not be able to use the definitions without licensing or permission if you are using the definitions in a work for profit.
You have to remember that not only is the dictionary is a work that is copyrighted, but each definition is an individual work that is copyrighted.
There are open source dictionaries that you can use. Check the license. It actually sounds like the WordNet and other semantics ontologies would be better for your use.
How (il)legal is it to get data from a 100% accessible but not "exposed" API