I feel that there is no really good way for practicing definitions at the moment. The self review doesn't really cut it, since its not really an exercise, but more of an self grading system, and to grade yourself can be pretty hard sometimes.
How about a 填空 (fill in the blanks) exercise? You would get a Chinese example sentence with a blank in it, just like how the example sentences usually look, like 你__然敢做出这种事来。(This example is for single characters)
Now, instead of tones or ratings at the 12345 buttons, you would get random characters to chose from. If you want to make it even harder for the single character version, you could have characters with the same pronunciation, like: 1.静 2.净 3.镜 4.竟 5.敬
Obviously, the correct answer is 4.
Of course, this would work with words too, like: 我____喜欢这种天气
1.中国 2,绿色 3.医生 4. 无聊 5.非常
What you would need to implement this is:
Random words (we already got them)
Random example sentences (we already got them)
The great thing about this way of studying is that you don't just learn what the word means, but you also understand the meaning of the whole sentence, and most importantly: understand how the word can be used.
Also, since we have so many example sentences, and hopefully we will be able to add new ones ourselves soon, you probably will learn new ways to use the word and see new sentences all the time.
One complication with this method would be that sometimes 2 answers could be correct. Not so much with the one character version, but in the "word" version. Like the example sentence above. Most people would argue that 5. 非常 is obviously the best answer, but 3.医生 is not wrong. Luckily, with so many users that would be willing to help, and the great feedback system, we could probably sort those sentences out in a very short time.
What do you think guys(and girls^^)?