The Collaborative International Dictionary of English v.0.48:

Rhadamanthus \Rhad`a*man"thus\, prop. n. [L., fr. Gr. ???.]
   (Greek Mythol.)
   One of the three judges of the infernal regions;
   figuratively, a strictly just judge.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Rhadamanthus
    n 1: (Greek mythology) a judge of the dead in the underworld

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "Rhadamanthus":
   Aeacus, Aides, Aidoneus, Astraea, Cerberus, Charon, Cora, Despoina,
   Dike, Dis, Dis pater, Erebus, Hades, Hel, Jupiter Fidius, Justice,
   Justitia, Kore, Loki, Minos, Nemesis, Orcus, Osiris, Persephassa,
   Persephone, Pluto, Pontius Pilate, Proserpina, Proserpine, Satan,
   Solomon, Themis, blindfolded Justice