The title sounds similar to Jimmy, and I think a few might be right in saying it could be a nickname. He might have made it up to sound like a nickname, referencing Jimmy, while using more of the word's meaning, as mentioned in other Jambi theories on here.
Lyrically, it's got many similarities to Jimmy as well.

Shine on forever
Shine on benevolent son
Shine down upon the severed
Shine until the two become one

Hold your light,
Eleven. Lead me through each gentle step by step
By inch by loaded memory
'till one and one are one, eleven,
So glow, child, glow.

It definitely feels as if Jimmy's 'one and one are one' is Maynard and Jimmy becoming one, though there was mention that the 'two become one' in Jambi could mean one without the other, more of a separation, both parties possibly being Jambi and Marie's separation through Marie's medical problems.

The fact that the song is followed by Wings for Marie and 10,000 Days also shines some light on this one. Judith Marie passed away approximately 10,000 days after Jimmy was eleven. The lyrics in the two songs are definitely about her passing. The three songs in sequence flow in a timeline as such. At eleven, Jambi/Jimmy's mother suffered from a stroke (as someone mentioned here anyway), thus a separation from Jambi and Marie, until 10,000 days later, the two are mortally separated by her death.

They lyrics make the same sort of allusions to Jimmy as well:

I'm coming back home.

It's time for you to bring me home.

However, they seem to be from different voices, as before. In 10,000 Days, it seems as if Judith Marie is the one who would be brought home, to heaven. The use of her name Marie is also for religious purpouses, though unlike Judith, Marie is used for the name as a mother and holy figure. Though that would make Jambi Jesus... anyway, an overly-zealous Tool fan can deal with that in another thread.

As for the lyrics of this song entirely, it seems as if he's speaking of the great life he has, though I'm not sure if that's before his mother's death or her earlier medical problems, and I'm not sure if if he's saying that he'd give anything for one more day with her before or after the medical problems. I'm still very confused about many aspects of this song, but I'm sure it's between him and his mother, not his son.

Sorry for the long, useless, confused post.

Fun.

I have no idea what Jambi is about so that sounds good

Nice insight.