The first official word, for the books, folks, is "car." Hilariously, it comes out like "caca".
It was a pair of socks that inspired him - this new pair has a little yellow car on them and so I pointed them out. He immediately said "caca" in his growly monster voice and I thought, that's pretty funny, but really figured it was a fluke. However, I kept saying it, and he kept repeating it, in that same growly voice, and then I took him into the next room, where his little toy car was, and pointed to that and said "caca". He repeated me. Finally, he said it on his own, looking at the toy car. He did it a couple more times later, as we were preparing for naptime. But I really knew it had sunk in when we took him in our real car this afternoon and he saw his little matchbox car on his seat. I heard a little, under the breath mutter: "ca!"
Hooray! Funny how that little milestone makes me feel on top of the world. I've been smiling all afternoon. Just shows you how your perspective totally changes when you become a parent. You appreciate everything so much more.