Long time ago, last century, when I was learning one more foreign language, I used card with words: with a word on one side, and its translation - on opposit side. The cards' size was exactly to matchbox, so it was comfortably to put the cards into pocket and to learn words every free minute - in a transport, for example.
The download of this application is 100% secure. Georgiy Golubyev has created the app that lies within the Educational category. Google Play shows that Palabras_lite is rated 4.7 by its users.