Definition: [noun] A quadruplex telegraph.
Definition: [noun] A house or apartment that has four rooms.
Definition: [noun] An apartment that has four floors connected by interior staircases.
Definition: [noun] A building divided into four separate residences; = "quadplex".
Definition: [adjective] Fourfold.
Definition: [adjective] Originally: designating a system of telegraphy enabling four messages to be sent over a wire at the same time, two in each direction (now chiefly historical). Later also: relating to or designating the transmission or reception of four signals simultaneously over one channel or with one aerial.
Definition: [adjective] Of a polyploid individual: having the dominant allele of a particular gene represented four times.