ebb / eb/ • n. (usu. the ebb) the movement of the tide out to sea: I knew the tide would be on the ebb [as adj.] the ebb tide. • v. [intr.] (of tidewater) move away from the land; recede: the tide began to ebb.Compare with flow. ∎ fig. (of an emotion or quality) gradually lessen or reduce: my enthusiasm was ebbing away.PHRASES: at a low ebb in a poor state: the country was at a low ebb due to the recent war.ebb and flow a recurrent or rhythmical pattern of coming and going or decline and regrowth.

ebb sb. OE. ebba = (M)LG., MDu. ebbe (Du. eb(be)) :- WGmc. *abjan-, -ōn, f. *ab (see OF), as if ‘a running off or away’.
So ebb vb. OE. ebbian = (M)LG., (M)Du. ebben.