WordNet (r) 3.0 (2006):

mutual understanding
    n 1: sympathy of each person for the other [syn: mutual
         understanding, mutual affection]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "mutual understanding":
   acclamation, accord, accordance, agreement, agreement of all,
   chorus, common assent, common consent, compact, concert, concord,
   concordance, concurrence, consensus, consensus gentium,
   consensus of opinion, consensus omnium, consent, consentaneity,
   consortium, cordial understanding, entente, entente cordiale,
   general acclamation, general agreement, general consent,
   general voice, harmony, like-mindedness, meeting of minds,
   one accord, one voice, same mind, single voice, total agreement,
   unanimity, unanimousness, understanding, unison,
   universal agreement