The Collaborative International Dictionary of English v.0.48:

Themis \The"mis\, n. [L., fr. Gr. ?, fr. ? that which is laid
   down or established by usage, law, prob. fr. ? to set,
   place.] (Gr. Myth.)
   The goddess of law and order; the patroness of existing
   rights.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Themis
    n 1: (Greek mythology) the Titaness who was goddess of justice
         in ancient mythology