Lewis & Short

fictĭo, ōnis, f. [fingo] (post-Aug.; esp. freq. in Quint.).

  1. I. A making, fashioning, forming, formation (cf.: confictio, figmentum): (animalis) fictio a capite sumit exordium, Lact. Opif. D. 12: hominis, i. e. creation, id. 4, 4; 2, 9: nominum fictio adjectis, detractis, mutatis litteris, Quint. 6, 3, 53; 8, 3, 19; [?*)ONOMATOPOII = /A ?], id est fictio nominis, id. 8, 6, 31; 9, 1, 5: Furium, veterem poëtam, dedecorasse linguam Latinam hujuscemodi vocum fictionibus, quae, etc., Gell. 18, 11, 2.
  2. II. In partic.
    1. A. A feigning, counterfeiting, disguising: in figura totius voluntatis fictio est, apparens magis quam confessa, Quint. 9, 2, 46: poëtarum, fictions, Lact. 1, 21 fin.: fictiones personarum, quae [?PROSWPOPOII = /AI ?] dicuntur, Quint. 9, 2, 29: personae, id. 9, 3, 89; 11, 1, 39; Vulg. Sap. 7, 13.
    2. B. Rhet. t. t., an assumed or fictitious case, a supposition, fiction: adhuc est subtilior illa ex simili translatio, cum, quod in alia re fieri solet, in aliam mutuantur. Ea dicatur sane fictio, Quint. 6, 3, 61; cf.: duci argumenta non a confessis tantum, sed etiam a fictione, quod Graeci καθ’ ὑπόθεσιν vocant, id. 5, 10, 95 Spald.: est et illa ex ironia fictio, qua usus est C. Caesar, etc., id. 6, 3, 91.
    3. C. Jurid. t. t.: fictio legis, a fictitious assumption in a case, a fiction, Gai. Inst. 3, 56; Dig. 35, 2, 1, § 1; 18; 41, 3, 15. For an account of the fictions in use in the formulas of the Roman law, v. Gai. Inst. 4, 32-38; cf. Savigny, Du Droit Romain, 5, pp. 76-84.