A duplex house is a single building that has two separate living spaces for two different families to live in. But sometimes, using the same word over and over again can become repetitive and boring. To add some variety to your vocabulary, you can use synonyms for the word "duplex house". Such synonyms could be "semi-detached house", "twin house", or "double residence". Depending on the region, it could also be called a "double-house", "two-family house", or even a "double-decker house". Regardless of whatever name you choose, be sure to remain consistent throughout your writing and always keep your reader in mind.