When you choose a longer or less straightforward way of saying something, you use periphrasis. One example of periphrasis is describing someone as "more intelligent" instead of "smarter."
Choosing a two-word description instead of the one-word equivalent (like "more lengthy" rather than "longer") is one way to use periphrasis. This also happens when you use a longer phrase, like "give a presentation," instead of a single word that conveys the same meaning, "present." Using many words to describe something instead of a simple noun is also periphrasis: "the mother of my father," for example, instead of "grandmother." The Greek root, periphrazein, means "speak in a roundabout way."