The Collaborative International Dictionary of English v.0.48:

Sinecure \Si`ne*cure\, n. [L. sine without + cura care, LL., a
   cure. See Cure.]
   1. An ecclesiastical benefice without the care of souls.
      --Ayliffe.
      [1913 Webster]

   2. Any office or position which requires or involves little
      or no responsibility, labor, or active service.
      [1913 Webster]

            A lucrative sinecure in the Excise.   --Macaulay.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sinecure \Si"ne*cure\, v. t.
   To put or place in a sinecure.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sinecure
    n 1: a benefice to which no spiritual or pastoral duties are
         attached
    2: an office that involves minimal duties

Bouvier's Law Dictionary, Revised 6th Ed (1856):

SINECURE. In the ecclesiastical law, this term is used to signify that an
ecclesiastical officer is without a charge or cure.
     2. In common parlance it means the receipt of a salary for an office
when there are no duties to be performed.