Figura etymologica is a rhetorical figure in which words with the same etymological derivation are used in the same passage. To count as a figura etymologica, it is necessary that the two words be genuinely different words and not just different inflections of the same word. For example, the sentence Once I loved, but I love no more is not a figura etymologica since although love and loved are obviously etymologically related, they are really just inflections of the same word. That makes this sentence a polyptoton.