You can't search 3-letter words by themselves, but if you add an asterisk, either in front of the word or behind the word, you'll get results.
Someone mentioned the word "air" on another thread. If you use *air with the asterisk in front of the word, you'll get everything that ENDS with air, like chair. If you use air* with the asterisk after the work, you'll get everything that begins with "air", including air. Try it with *cam and cam*. You'll get different results. Same with *oil and oil*.

Hope this helps.