Aa or a'a

It seems to be a common misconception that the first word in the dictionary is "aardvark." This is, of course, untrue; the first word in the dictionary is "a." Naturally. Aardvark isn't even in the first column.

After the various versions of "a" and a couple prefixes and abbreviations comes the first multi letter word in the dictionary: aa or a'a. According to the AHD this word means "Lava having a rough surface, and it comes from the Hawai'ian "'a'a" to burn. I'm not sure why we needed a word for this, but it's useful in Scrabble, if nowhere else.