ebb and flow

/EH1 B AH0 N D F L OW0/
noun
  1. 1

    The flowing out and in of the tide.

  2. 2

    A large flowing out and in.

    โ€œ2001: I want to hear the roaring ebb and flow of Broadway โ€” The New Yorker Online, 29 Oct 2001โ€

verb
  1. 1

    To alternately ebb and flow.

Source: https://en.wiktionary.org/wiki/ebb%20and%20flow