Expand your vocabulary with Knoword.
You’ll be given a definition and the first letter of a word. Type in the answer. If you start typing incorrect letters, they will turn red. They’ll stay green if you’re correct. The time limit is 1 minute, but each time you answer a word correctly, you are awarded an extra 5 seconds.
You can skip a word (click on the X), and it will tell you the answer, but you’ll lose 10 points.
You can choose from three levels of difficulty: Novice, Hotshot and Wizard
You don’t need to sign up or log in to play, but if you want to be on the leaderboard, you should sign up.
There’s an app, too, though it’s not free (¥120). But the regular website works fine on a smart phone or tablet. I did not try the app.
Good point: there’s a pretty wide variety in level of difficulty, even in the Novice category. Examples of simple words that most EFL students would get right away: baseball, friend, grape. Some more challenging words: Sabbath, gopher, debunk.
Bad point: if you run out of time, unless you quickly hit the X, you won’t discover the answer to that last question, which can be frustrating. But if you take a quick screenshot of the definition, you can think about it (or ask someone for help) later.
Notable: The site uses British spelling. So, for example, it’s “colourful” and not “colorful”.