Lewis & Short

dēcessĭo, ōnis, f. [decedo], a going away, departure (opp. accessio—good prose).

  1. I. Lit.
    1. A. In gen.: is mecum saepe de tua mansione aut decessione communicat, Cic. Fam. 4, 4 fin.
    2. B. Esp.
      1. 1. The withdrawal, retirement of a magistrate from the province he has governed, Cic. Pis. 36, 89; id. Att. 6, 5 fin.; id. Q. Fr. 1, 1, 1.
      2. 2. Pregn., the decrease, diminution, abatement, or entire disappearance of an object: neque enim ulla decessio fieri poterat neque accessio, Cic. Univ. 6: utrum accessionem decumae an decessionem de summa fecerit, id. Rab. Post. 11, 30 sq.; Dig. 29, 4, 28 fin.: decessio capitis aut accessio, Cic. Div. 2, 15, 36: accessio et decessio febris, Cels. 3, 3 fin.; so id. 2, 4 et saep.
      3. 3. Decease: Juliani, Spart. Did. Jul. 7 fin.
  2. * II. Trop.: verborum, the transition, transferring of words from their primary to a derivative meaning, Gell. 13, 29, 1.