(US, Canada) A house made up of two dwelling units.

(US) A dwelling unit with two floors.

(philately) A cancellation combining a numerical cancellation with a second mark showing time, date, and place of posting.

(juggling) A throwing motion where two balls are thrown with one hand at the same time.

(biochemistry) A double-stranded polynucleotide.

(geology) A system of multiple thrust faults bounded above and below by a roof thrust and floor thrust.

To make duplex.

To make into a duplex.

(juggling) To make a series of duplex throws.

An adjective "duplex" is used to describe something that is double or made up of two parts, such as a building with two floors, two units, or a structure containing austenite and ferrite in equal proportions.

(telecommunications) Bidirectional (in two directions).

(soil science) Having horizons with contrasting textures.