Is there an English-English online dictionary with the ability to save a list of learned words?

Question

English learning tools

Guys, please answer, does such a web service (English-English dictionary) exist in nature, which:
1) Allows you to save words and their meanings in a list of the form: You are

interested in just such a format in which you do not need to go somewhere to find out the meaning of the stored word.
2) The service must be free.
3) Having an app for Android/iOS is a big plus.

Answer 1

I don’t know about one, but these two can be adapted for this business.
Here we get words for study from any text wordsfromtext.com
And here we make them cards english-cards.ru