The Collaborative International Dictionary of English v.0.48:

Ebb \Ebb\, n. [AS. ebba; akin to Fries. ebba, D. eb, ebbe, Dan.
   & G. ebbe, Sw. ebb, cf. Goth. ibuks backward; prob. akin to
   E. even.]
   1. The reflux or flowing back of the tide; the return of the
      tidal wave toward the sea; -- opposed to flood; as, the
      boats will go out on the ebb.
      [1913 Webster]

            Thou shoreless flood which in thy ebb and flow
            Claspest the limits of morality!      --Shelley.
      [1913 Webster]

   2. The state or time of passing away; a falling from a better
      to a worse state; low state or condition; decline; decay.
      "Our ebb of life." --Roscommon.
      [1913 Webster]

            Painting was then at its lowest ebb.  --Dryden.
      [1913 Webster]

   Ebb and flow, the alternate ebb and flood of the tide;
      often used figuratively.
      [1913 Webster]

            This alternation between unhealthy activity and
            depression, this ebb and flow of the industrial.
                                                  --A. T.
                                                  Hadley.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "ebb and flow":
   Lissajous figure, alternate, alternation, back and fill,
   back-and-forth, battledore and shuttlecock, be poised, billow,
   break, comb, come and go, coming and going, crash, dash,
   direct tide, ebb, ebb tide, flood, flood tide, flounder, flow,
   fluctuate, flux, flux and reflux, full tide, go through phases,
   heave, high tide, high water, hitch and hike, lift, low tide,
   low water, lunar tide, neap, neap tide, opposite tide, oscillate,
   pass and repass, peak, pendulate, popple, reciprocate,
   reciprocation, refluence, reflux, rhythmic play, ride and tie,
   ring the changes, rip, riptide, rise, rise and fall, roll, scend,
   seesaw, seesawing, send, shift, shuffle, shuttle, shuttlecock,
   sine wave, smash, solar tide, spring tide, stagger, surge, sway,
   swell, swing, teeter, teeter-totter, teeter-tottering, teetering,
   thalassometer, tidal amplitude, tidal current, tidal current chart,
   tidal flow, tidal range, tide, tide chart, tide gate, tide gauge,
   tide race, tide rip, tidewater, tideway, to-and-fro, toss, totter,
   tottering, turn, undulate, ups and downs, vacillate, vary, wave,
   waver, wax and wane, wibble-wabble, wigwag, wobble, zigzag