silent second
n.—Gloss: Someone who loans money to someone else in order to buy a home, usually to make them look like a good risk, without notifying the prime lender. «The holdback could be considered what is known as a silent second, which is illegal. Many private lenders have gone to jail in the past because they lent money to a homebuyer to assist in the purchase but did not advise the prime lender of this fact.» —“Owners have options in lease-to-own deals” by Benny L. Kass Richmond Times-Dispatch (Virginia) Mar. 8, 2009. (source: Double-Tongued Dictionary)
Further reading
In the thriller Down Cemetery Road starring Emma Thompson, a character uses the Briticism safe as houses, meaning “quite safe,” an expression thought to derive either from the sturdiness of a house or the sense of real estate as a secure investment...
While reading Great Expectations (Bookshop|Amazon) by Charles Dickens, a listener in Arlington, Texas, is surprised when one of the characters inherits some money, which Dickens describes as a cool four thousand. Were they really using cool that way...