Lewis & Short

portĭo, ōnis (abl. sing. portioni, Inscr. Lat. 206, 38), f. [kindr. with pars and πόρω, to share, impart], a share, part, portion (post-Aug., except in the phrase pro portione; v. in foll. II.).

  1. I. Lit.: Luna aequā portione divisa, Plin. 2, 9, 6, § 42: ex his portio in Italiā consedit, portio in Illyricos sinus penetravit, Just. 24, 4, 2: hereditatis, id. 36, 2, 5; cf. id. 21, 1, 2: quamvis quota portio faecis Achaei, Juv. 3, 61: mox in proflatum additur tertia portio aeris collectanei, Plin. 34, 9, 20, § 97: pari portione inter se mixta pix, cera, alumen, etc., Cels. 4, 24; cf.: glandis cortex et nitrum paribus portionibus, id. 5, 18, 4: nil natura portionibus parit, by parts, piecemeal, Plin. 17, 22, 35, § 177: portio brevissima vitae, Juv. 9, 127: pars A carnaniae, quam in portionem belli acceperat, as his share for his services in the war, Just. 28, 1, 1: vocare aliquem in portionem muneris, id. 5, 2, 9: magna mortalium portio, Plin. 8, 28, 42, § 102.
  2. II. Transf., a relation to any thing, proportion, i. q. proportio.
    1. A. In gen., adverb.
      1. 1. prō portiōne (class.; not in Cæs.), in proportion, proportionally, relatively: pro portione ea omnia facito, Cato, R. R. 106 fin.: pro portione ad majorem fundum vel minorem addere, Varr. R. R. 1, 18, 3: Mamertinis pro portione imperaretur, Cic. Verr. 2, 5, 21, § 55; id. Fl. 14, 32; Liv. 34, 50: oportet ut aedibus ac templis vestibula et aditus, sic causis principia pro portione rerum praeponere, in relation, in proportion, Cic. de Or. 2, 79, 320; so, pro ratā portione, Plin. 11, 15, 15, § 40: pro suā scilicet portione, Quint. 10, 7, 28; Censor. de Die Nat. 3.
      2. 2. portĭōne (post-Aug.): cerebrum omnia habent animalia, quae sanguinem: sed homo portione maximum, proportionally, Plin. 11, 37, 49, § 133; so id. 11, 37, 70, § 183; 11, 2, 1, § 2; cf.: hac portione mediocribus agris semina praebenda, Col. 2, 9, 1: quādam portione, Quint. 6, 1, 26: eādem portione, id. 11, 3, 139.
      3. 3. ad portiō-nem (rare and only post Aug.), Plin. 14, 21, 27, § 133; 24, 8, 30, § 46: ad suam quisque portionem, id. 36, 16, 25, § 9: supra portionem, Col. 7, 1, 2.
    2. B. Subst.: eadem ad decem homines servabitur portio, the same proportion, Curt. 7, 11, 12: portionem servare, Col. 11, 2, 87; cf.: proportione servatā, id. 8, 11, 6.