The Collaborative International Dictionary of English v.0.48:

Ebb \Ebb\, v. i. [imp. & p. p. Ebbed; p. pr. & vb. n.
   Ebbing.] [AS. ebbian; akin to D. & G. ebben, Dan. ebbe. See
   2d Ebb.]
   1. To flow back; to return, as the water of a tide toward the
      ocean; -- opposed to flow.
      [1913 Webster]

            That Power who bids the ocean ebb and flow. --Pope.
      [1913 Webster]

   2. To return or fall back from a better to a worse state; to
      decline; to decay; to recede.
      [1913 Webster]

            The hours of life ebb fast.           --Blackmore.

   Syn: To recede; retire; withdraw; decay; decrease; wane;
        sink; lower.
        [1913 Webster]

WordNet (r) 3.0 (2006):

ebbing
    n 1: a gradual decline (in size or strength or power or number)
         [syn: ebb, ebbing, wane]