Third person singular present tense of 'ebb,' meaning decreases, flows backward, or gradually weakens.
From Old English 'ebba,' with the present tense '-s' suffix for third person singular. The meaning has extended from tides to any gradual decline.
The phrase 'ebb and flow' is so common we barely notice it, but it's based on our observation that the most powerful force on Earth — ocean tides — moves in reversible cycles.
Complete word intelligence in one call. Free tier — 50 lookups/day.