Lewis & Short

accessĭo, ōnis, f. [accedo], a going or coming to or near, an approach.

  1. I. In gen.: quid tibi in concilium huc accessio est? why comest thou hither? Plaut. Trin. 3, 2, 86; cf.: quid tibi ad hasce accessio est aedīs prope? id. Truc. 2, 2, 3; Cic. Univ. 12: ut magnas accessiones fecerint in operibus expugnandis, sallies, Caes. B. Alex. 22: suo labore suisque accessionibus, i. e. by his labor of calling on people, by his visits, Cic. Verr. 2, 2, 53 fin.
  2. II. In part.
    1. A. In medicine, t. t., the access, attack, or paroxysm of a disease, Cels. 2, 12; 3, 3 sq.; Sen. Ep. 85, 12; id. N. Q. 6, 18, 6; Suet. Vesp. 23 al.
    2. B. A coming to in the way of augmentation, an increase, addition.
      1. 1. In abstracto: paucorum annorum, Cic. Lael. 3, 7: pecuniae, Nep. Att. 14, 2: fortunae et dignitatis, Cic. Fam. 2, 1; 7, 6; 10, 9; id. Rep. 2, 21: odii, Caes. B. Alex. 48: dignitatis, Vell. 2, 130 fin.
      2. 2. The thing added, the addition, or accession: in concreto: Scaurusaccessionem adjunxit aedibus, added a new part, Cic. Off. 1, 39, 138; so id. Att. 16, 16. Thus Syphax is called, accessio Punici belli, as not being the chief enemy in the Punic war, but, as it were, an appendage to the war, Liv. 47, 7; so in Pliny: turbā gemmarum potamus—et aurum jam accessio est, and gold is only accessory, a mere appendage, 33 prooem. fin.
    3. C. In rhetor., an addition that makes a definition complete: nisi adhiberet illam magnam accessionem, Cic. Ac. 2, 35, 112; so id. Fin. 2, 13.
    4. D. The addition to every kind of fee or tax (opp. decessio), Cato R. R. 144: decumae, Cic. Rab. 11; so id. Verr. 2, 3, 33, § 116 al.