You look up a word, it is exactly right, and a week later it is gone again. The good ones never stick.
So keep them. Every entry now has an "Add to My Dictionary" button. Tap it, and the word is saved.
Add words, phrases, idioms, whatever you want to remember. Keep what you like, remove what you don't. It is your list.
Three weeks into Spanish, and the word for tomorrow keeps slipping. Look up mañana once, save it, and it stops slipping for good.
It is free. All your words, in one place.