make a dent in
make a dent in {v. phr.}, {informal}
To make less by a very small amount; reduce slightly. — Usually used in the negative or with such qualifying words as "hardly" or "barely".
John shoveled and shoveled, but he didn't seem to make a dent in the pile of sand.
Mary studied all afternoon and only made a dent in her homework.
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Source: A Dictionary of American Idioms
