Pleonasm, which stems via Late Latin from the Greek verb pleonazein ("to be excessive"), is a fancy word for "redundancy." It's related to our words "plus" and "plenty," and ultimately it goes back to the Greek word for "more," which is "pleōn." Pleonasm is commonly considered a fault of style, but it can also serve a useful function. "Extra" words can sometimes be helpful to a speaker or writer in getting a message across, adding emphasis, or simply adding an appealing sound and rhythm to a phrase - as, for example, with the pleonasm "I saw it with my own eyes!" - https://www.merriam-webster.com/dictionary/pleonasm