Duplex is Latin for "double". It literally means "twofold".
Duplex commonly means double or twofold. It can also mean a two floor apartment.
I wouldn't use them interchangeably. If something is twofold, it has two steps or parts as in a twofold solution. On the other hand is an expression we use to introduce a contradiction or alternative: if we buy the less expensive freezer, we will save money now; on the other hand, we may spend more in the long run by having higher energy costs. The two terms cannot be used interchangeably in these sentences.
twofold doubleheader
A message that contains two meanings.
Other words for "twofold" (also two-fold) are dual, double, paired, coupled, or twin. (e.g. a twofold reason for proceeding)In math, a twofold increase simply means that a rate has doubled.
coupled, paired, twin, duplicate, dual, twofold
coupled, paired, twin, duplicate, dual, twofold
double, doubly, once over, over again, twofold
twofold, double, twin, matched, paired, duplicate, binary, duplex
Some words that end with the suffix -fold are twofold, threefold, manifold, and sevenfold.
Chinese the foods are twofold believes. High of grain and around the back.