The Collaborative International Dictionary of English v.0.48:

Longanimity \Lon`ga*nim"i*ty\, n. [L. longanimitas; longus long
   + animus mind: cf. F. longanimit['e].]
   Disposition to bear injuries patiently; forbearance;
   patience. --Jer. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

longanimity
    n 1: good-natured tolerance of delay or incompetence [syn:
         patience, forbearance, longanimity] [ant:
         impatience]

The Devil's Dictionary (1881-1906):

LONGANIMITY, n.  The disposition to endure injury with meek forbearance
while maturing a plan of revenge.