ebb
noun /eb/
  /eb/
the ebb
 [usually singular]Idioms - the period of time when the sea flows away from the land- the ebb tide
 Extra Examples- It was difficult sailing upstream against a strong ebb.
- They left port on the ebb tide.
- They went out to sea with the ebb.
 Oxford Collocations Dictionaryebb + noun- tide
 - against an/the ebb
- on an/the ebb
- with an/the ebb
- …
 - the ebb and flow of something
 Word OriginOld English ebba (noun), ebbian (verb), of West Germanic origin; related to Dutch ebbe (noun), ebben (verb), and ultimately to of which had the primary sense ‘away from’.
Idioms 
at a low ebb 
- in a poor state; worse than usual- Morale among teachers is at a low ebb.
 
the ebb and flow (of something/somebody) 
- the repeated, often regular, movement from one state to another; the repeated change in level, numbers or amount- the ebb and flow of the seasons
- She sat in silence enjoying the ebb and flow of conversation.
- He had known her long enough to recognize the ebb and flow of her moods.
- the natural ebb and flow of water
- We see a constant ebb and flow of jobs.