Word origin - Jamboree

I notice that the word "Jamboree" shows up in dictionary lists as having unknown origin. I'd like to venture a guess... and see what anyone thinks:

The origin must have originated with Robert Baden-Powell, who was the founder of the Boy Scouts. Baden-Powell lived in Kenya, East Africa. I recall hearing stories of how he admired the "native" Africans, and some of the Boy Scout traditions originated from African tribes.

Any way... the Swahili word for "hello" is "jambo". A "jamboree" is certainly a gathering of people all saying "hello" or "jambo" to each other.

Has anyone heard this before?

It sounds reasonable. Has anyone read a biography of Baden-Powell? There might be substantiation there.

Looks like the word may be older than Scouting.
Merriam Webster online says the word dates back to 1864. An online quotes Baden-Powell about early days: "Somewhere about 1893 I started teaching Scouting to young soldiers in my regiment." www.pinetreeweb.com/ bp-listener.htm