Learn A Word: Sound
Seeing the title, you are probably thinking: I knew this word! Well, let's check: Do you know what the "Puget Sound" is? What about the "Prince William Sound"?
If you don't know the meaning of "sound" in these two case, you are not alone. Actually, while traveling at the Prince William Sound, I had to ask the captain of our boat in order to understand it. Here is the captain's explanation:
"A sound is a large, complex body of water with multiple entrances and exits."
As it turned out, the captain's explanation is even better than Wiktionary's definition! Compare the above with the definition of sound under Etymology 3 at Wiktionary. There is a good picture of the Puget Sound by NASA on Wikipedia in the same entry. See for yourself!