ebb
n.
Old English ebba "falling of the tide, low tide," perhaps from Proto-Germanic *af- (cognates: Old Frisian ebba, Old Saxon ebbiunga, Middle Dutch ebbe, Dutch eb, German Ebbe), from PIE root *apo- "off, away" (see apo-). Figurative sense of "decline, decay, gradual diminution" is from late 14c. Ebb-tide is from 1776.
v.
Old English ebbian "flow back, subside," from the root of ebb, n.. Figurative use in late Old English. Related: Ebbed; ebbing.