Disagreeable?
You're the one who keeps disagreeing with people.
Many people have given you their definitions for the dollar, and you predicate everything with this: "To me, the "dollar" still seems somewhat imaginary...an "IOU-nothing"
That tells me that the only thing you're really looking for are definitions that SUPPORT your version of what the dollar is. If it doesn't match what you want to hear, you reject it.
Have you ever really LOOKED at a dollar bill?
This statement is on the front, and is on the front of every US bill: "This note is legal tender for all debts, public and private."
As a tender issue by the Government, it is, to quote a quote, backed by the full faith and trust of the US Government.
FAITH.
TRUST.
That means that your dollar isn't backed by a comparable quantity of a tangible good, such as gold. It's not a gold or a silver certificate bill.
It means, as I said, that the currency of the United States is a CONCEPT. That WE accept it, and use it, instead of going to a goods for services barter system (I wonder how many chickens it would take to pay my mortgage) means that we also accept the concept that the US dollar has value that exceeds that of the ink, cloth, and labor that goes into producing it.
Obviously, though, none of these definitions really meets your "gold standard" so to speak.