Lewis & Short

sācōmārĭus, a, um, adj. [sacoma], serving for a counterpoise, used for a weight in a balance: cucurbitae, Hier. in Jon. 4, 6.
Hence, substt.

  1. A. sācōmārĭus, ii, m., one who makes counterpoises or weights in gen.; called also PONDERARIVS, Inscr. Orell. 4274.
  2. B. sācōmārĭum, ii, n., the public balance or weighing place, Inscr. Orell. 4109; 7194.