Is cash(currency) a security and a debt instrument? I know that cash is a financial asset and securities are defined as tradable financial assets, so cash is a security, right?
Another thing I'm wondering is that whether cash/banknote is a debt instrument or not. On wikipedia it is defined as one of a debt securities.
I don't think cash could be described as a security... one of the characteristics of securities is that they have imperfect (if very high) liquidity and provide a return (be it fixed or variable). Cash is the definition of liquid and inherently provides no return - you could earn interest on cash by depositing it in a bank but then you are creating a debt obligation in effect - the cash inherently, as in cash in a physical safe, generates zero return nominal by definition. You could think of cash as a debt security where a debt is theoretically placed on the issuer. But: in practice the debt is impossible to pay. You cannot bring a bill into the fed and demand they honour it. So I suppose it would be a debt security in the theoretical sense but it lacks almost all properties of debt securities:
cannot be repaid in practice, never intended to be repaid, perfectly liquid etc, and it has a value that cannot be expressed in terms of anything but itself.