(idiomatic) A person or thing whose nature or value is a mystery. / Used other than figuratively or idiomatically: see unknown, quantity.

The next bluff in sequence after a double bluff and a triple bluff

To perform a quadruple bluff

plural of quadratic function

plural of quantum Hall effect

Alternative spelling of buttonquail

(economics) A monetary policy in which the central bank increases the money supply in the banking system, as by purchasing bonds from banks.

plural of quadruple star system

plural of quadruple star

(astronomy) A stellar system that has four stars orbiting around each other; quadruple star