an estimation that is too low; an estimate that is less than the true or actual value
make too low an estimate of; "he underestimated the work that went into the renovation"; "Don't underestimate the danger of such a raft trip on this river"
marked by excessive confidence; "an arrogant and cocksure materialist"; "so overconfident and impudent as to speak to the queen"; "the less he knows the more positive he gets"