Lewis & Short

dērīvātĭo, ōnis, f. [derivo], a leading off, turning off, turning away.

  1. I. Lit.: derivationes fluminum, * Cic. Off. 2, 4, 14: sollemnis (sc. lacus Albani), Liv. 5, 15 (cf. shortly before, priusquam ex lacu Albano aqua emissa foret).
  2. II. Trop.
    1. A. In gen.: dictum aliquod in aliquem usum tuum opportuna derivatione convertere, Macr. S. 6, 1.
    2. B. Esp.
      1. 1. In grammat. lang., derivation, etymology of words, Plin. ap. Serv. Aen. 9, 706; Dig. 50, 16, 57; Charis. p. 73 P. et saep.
      2. 2. In rhetor.
          1. (α) An exchanging of one word for another of like meaning, to soften the expression (as fortis for temerarius, liberalis for prodigus, etc.), Quint. 3, 7, 25.
          2. (β) As rhet. fig. = παρηγμένον, the development of a preceding statement or conception into a new thought, Jul. Ruf. Schem. Lex. § 14.