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noun tide·mark \-ˌmärk\

Simple Definition of tidemark

  • : a mark on the beach that shows how far the water came in toward the shore when the tide was high

  • : a mark left by dirty water in a bathtub

Source: Merriam-Webster's Learner's Dictionary

Full Definition of tidemark

  1. 1a :  a high-water or sometimes low-water mark left by tidal water or a floodb :  a mark placed to indicate this point

  2. 2 :  the point to which something has attained or below which it has receded <the tidemark of tolerance has risen — New Republic>

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