duplex

(noun) a house with two units sharing a common wall. Synonyms: duplex house, semidetached house.

(noun) an apartment having rooms on two floors that are connected by a staircase. Synonyms: duplex apartment.

(verb) change into a duplex.

(adj) (used technically of a device or process) having two parts. Example: "A duplex transaction."

(adj) allowing communication in opposite directions simultaneously. Examples: "Duplex system." "Duplex telephony."