LATIN DICTIONARYLexicon Latīnum
noun · neutersecond declension

portōrium

portōrium n (genitive portōriī or portōrī)

Meaning

  1. port duty, levie paid by ships to finance upkeep of public harbours
  2. 1/40 (2.5%) custom-tax on trade between Roman provinces

Latīnē defined in Latin in our graded readers

Declension

declension
formsingularplural
nominativeportōriumportōria
genitiveportōriī
portōrī		portōriōrum
dativeportōriōportōriīs
accusativeportōriumportōria
ablativeportōriōportōriīs
vocativeportōriumportōria

portōrĭum (
I. dat. plur. PORTORIEIS, Plebisc. Thermens ap. Orell. 3673), ĭi, n. root por, whence porto, portitor, portus, that belongs to carrying or conveying; hence,
I. A tax, toll, duty, impost paid on goods imported or exported: portorium dare, Lucil. ap. Non. 37, 20; Cic. Verr. 2, 2, 72, § 176; 2, 2, 75, § 185; id. Font. 5, 19; id. Pis. 36, 87; Caes. B. G. 1, 18; 3, 1; Liv. 39, 24; Plaut. Trin. 4, 4, 15; Caecil. ap. Gell. 15, 14, 5; Dig. 19, 2, 60 fin.; cf.: ego pol istum portitorem privabo portorio, Plaut. As. 1, 3, 7: portorium circumvectionis, a tax paid for the right of hawking goods about the country, a peddler's tax, Cic. Att. 2, 16, 4.— *
II. Fare, freight, = naulum: Charon expetens portorium, App. M. 6, p. 180, 28.

Origins

From porta (“gate”), or, as it appears in Plautus, possibly from an earlier stage of the language having an equivalent etymology. Compare portitōrium.

In the Academy Smith's classical dictionaries

AntiquitiesPortoriumPortorium 1. Transit-dues or tolls on goods carried through a country or over a bridge, or a toll on travellers (Suet. Vit. 14; Seneca, de Const. Sap.…

Quick answers

What does portōrium mean in Latin?
portōrium, a noun, means “port duty, levie paid by ships to finance upkeep of public harbours; 1/40 (2.5%) custom-tax on trade between Roman provinces”.
What is the genitive of portōrium?
The genitive singular is portōriī. portōrium is neuter, second declension.