The Collaborative International Dictionary of English v.0.48:

Non-feasance \Non-fea"sance\, n. [Pref. non- + OF. faisance a
   doing, fr. faire to do.] (Law)
   An omission or neglect to do something, esp. that which ought
   to have been done. Cf. Malfeasance.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nonfeasance
    n 1: a failure to act when under an obligation to do so; a
         refusal (without sufficient excuse) to do that which it is
         your legal duty to do