I have found these terms related to the money or investment that does not grow or yield gains for the investor.
1- Dead money(slang): It could be money stashed in a mattress, non-interest yielding checking account or a security that does not yield returns. http://www.investopedia.com/ask/answers/08/dead-money.asp
2 -Idle capital: firm's unused money and propertythe money and assets of a business that are not being invested productively.
Related definitions of "idle capital": Also called barren money, sideline cash
3- Money on the sideline: The cash that is held either in savings or in low-risk, low-yield investment vehicles, such as certificates of deposits (CDs), instead of being placed in investments that have the potential for greater rewards, such as the stock market.
on the sidelines:not being used or not involved in an activity:
The absence of new products is keeping consumers on the sidelines.
stay/wait/sit on the sideline
▪️... sitting on mountains of “dead money,” the idle dollars on balance sheets that could instead feed economic growth
▪️Canadian companies have been accumulating “dead money” — cash sitting idle in bank accounts.
▪️Don't keep idle money in your bank account.