Figura etymologica is a
rhetorical figure in which words with the same
etymological derivation are used adjacently. Note that 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.