An appraisal that underestimates the value of something

Usage examples of underevaluation.

You will find, too, many data that have long been known by all, and you will possibly consider them far from news and be prone to under-evaluate them: be assured that underevaluation of these facts kept them from being valuable, no matter how long they were known, for a fact is never important without a proper evaluation of it and its precise relationship to other facts.