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.
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            That Power who bids the ocean ebb and flow. --Pope.
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   2. To return or fall back from a better to a worse state; to
      decline; to decay; to recede.
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            The hours of life ebb fast.           --Blackmore.

   Syn: To recede; retire; withdraw; decay; decrease; wane;
        sink; lower.
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The Collaborative International Dictionary of English v.0.48:

Ebb \Ebb\ ([e^]b), n. (Zo["o]l.)
   The European bunting.
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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.
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            Thou shoreless flood which in thy ebb and flow
            Claspest the limits of morality!      --Shelley.
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   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.
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            Painting was then at its lowest ebb.  --Dryden.
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   Ebb and flow, the alternate ebb and flood of the tide;
      often used figuratively.
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            This alternation between unhealthy activity and
            depression, this ebb and flow of the industrial.
                                                  --A. T.
                                                  Hadley.
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The Collaborative International Dictionary of English v.0.48:

Ebb \Ebb\, v. t.
   To cause to flow back. [Obs.] --Ford.
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The Collaborative International Dictionary of English v.0.48:

Ebb \Ebb\, a.
   Receding; going out; falling; shallow; low.
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         The water there is otherwise very low and ebb.
                                                  --Holland.
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WordNet (r) 3.0 (2006):

ebb
    n 1: a gradual decline (in size or strength or power or number)
         [syn: ebb, ebbing, wane]
    2: the outward flow of the tide [syn: ebb, reflux]
    v 1: flow back or recede; "the tides ebbed at noon" [syn: ebb,
         ebb away, ebb down, ebb out, ebb off] [ant:
         surge, tide]
    2: hem in fish with stakes and nets so as to prevent them from
       going back into the sea with the ebb
    3: fall away or decline; "The patient's strength ebbed away"

Moby Thesaurus II by Grady Ward, 1.0:

232 Moby Thesaurus words for "ebb":
   abate, ablate, advance, ascend, back, back up, bate, be eaten away,
   budge, calm, calm down, catabasis, cease, cessation, change,
   change place, circle, climb, collapse, comedown, consume,
   consume away, corrode, course, crash, crumble, dead set,
   dead stand, dead stop, deadlock, debasement, decadence, decadency,
   deceleration, declension, declination, decline, decline and fall,
   decrease, decrescendo, deformation, degeneracy, degenerateness,
   degeneration, degradation, deliquesce, demotion, depravation,
   depravedness, depreciation, derogation, descend, descent,
   deterioration, devolution, die, die away, die down, diminish,
   diminuendo, direct tide, dive, downtrend, downturn,
   downward mobility, downward trend, drift away, drop, drop off,
   dwindle, dwindling, dying, dying down, ease off, ebb and flow,
   ebb tide, ebbing, effeteness, erode, fade, fade away, fading, fail,
   failing, failure, failure of nerve, fall, fall away, fall off,
   falling-off, flood, flood tide, flow, flow back, flow in, flow out,
   flush, flux, flux and reflux, full stop, full tide, get over, go,
   go around, go away, go down, go downhill, go off, go round,
   go sideways, gush, gyrate, halt, high tide, high water,
   hit a slump, hit rock bottom, hit the skids, involution, issue,
   languish, lapse, lessen, let up, lock, loss of tone, low tide,
   low water, lull, lunar tide, make, melt away, moderate, molder,
   mount, move, move away, move off, move over, neap, neap tide,
   opposite tide, pacify, peter out, plummet, plunge, pour, progress,
   pull away, quiesce, quiet, quieten, reach the depths, recede,
   refluence, reflux, regress, regression, regurgitate, relent,
   remission, retire, retreat, retrocede, retrocession,
   retrogradation, retrograde, retrogress, retrogression, rip,
   riptide, rise, rotate, run, run down, run low, rush, sag, set,
   shift, shrink, sink, slacken, slide, slip, slippage, slowdown,
   slump, soar, solar tide, soothe, spin, spring tide, stand,
   stand off, standstill, stillstand, stir, stop, stream, subside,
   subsidence, surge, surge back, tail off, 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, touch bottom, tranquilize, travel,
   trend, wane, waning, waste, waste away, wear, wear away, whirl,
   widen the distance, withdraw