Figura etymologica is like when you use two words that sound similar to each other in a sentence to make it sound fancy or interesting.
For example, if you say "I fear fear itself," you are using figura etymologica because the words "fear" and "itself" sound alike.
It's like playing a word game with yourself where you try to find words that sound the same even though they have different meanings. It makes your sentences more fun to listen to and can make you sound smarter.