The Collaborative International Dictionary of English v.0.48:

Succussion \Suc*cus"sion\, n. [L. succussio, from succutere: cf.
   F. succussion. See Succussation.]
   The act of shaking; a shake; esp. (Med.), a shaking of the
   body to ascertain if there be a liquid in the thorax.
   [1913 Webster]

WordNet (r) 3.0 (2006):

succussion
    n 1: shaking a person to determine whether a large amount of
         liquid is present in a body cavity