MoreBlanks will improve your English.
MoreBlanks is a simple game to learn English words, it builds on the Blanks application (freely available on the Appstore). It contains over 10.000 words with three difficulty settings.
On the option screen, you can select the difficulty level.
To get to the option screen press the little i icon on the right side of the main screen over the word definitions.
Select the word you think fits the definition and drag it into the blank on top.