Barnwyr fel corff yw'r Farnwrniaeth[3], ynghyd ag ynadon ac ati. Mae'n ymgorffori pŵer y wladwriaeth.
Ym mhob gwlad ddemocrataidd heddiw mae o leiaf 3 phŵer sylfaenol, sef: Deddfwrfa, Gweithrediaeth, a Barnwriaeth. Ceir y cofnod cynharaf o'r gair Cymraeg "barnwriaeth" o'r 14g.[3]
↑Hamilton, Marci. God vs. the Gavel, p. 296 (Cambridge University Press 2005): "The symbol of the judicial system, seen in courtrooms throughout the United States, is blindfolded Lady Justice."
↑Fabri, Marco. The challenge of change for judicial systems, p, 137 (IOS Press 2000): "the judicial system is intended to be apolitical, its symbol being that of a blindfolded Lady Justice holding balanced scales."