Nana or more specifically NANANA! is one of Jack's favourite word/sounds right now. At first I'd encourage him by saying, "Nana isn't here right now" or bringing him a picture of my mom and pointing to it, or when my mom is around agreeing and pointing directly at her.
Last Friday, I was at my friend C's house and we discovered what Jack really means when he screams NANANA! I was enjoying a glass of white wine that Jack really wanted to get a hold of, no matter where we moved it to he would yell Nana and chase after it. We had a good laugh testing the theory and had to slow down when it became apparent that tears were imminent.
*As suggested (often) by my brother much to my mother's chagrin.
**They aren't nearly as original as my good friend E, who instead of Aunt E wants to be called Princess Unicorn or my (female) cousin K who wants to be called Uncle Jokes. Maybe letting people choose was a mistake.
***He still refuses to crawl like a normal baby and smacks the floor as hard as he can doing mini push-ups across the room to his intended destination.