Quick definitions from WordNet (underestimate)
▸ noun: an estimation that is too low; an estimate that is less than the true or actual value
▸ verb: make too low an estimate of ("He underestimated the work that went into the renovation")
▸ verb: make a deliberately low estimate
▸ verb: assign too low a value to ("Don't underestimate the value of this heirlooom-you may sell it at a good price")
▸ Also see underestimate
▸ noun: an estimation that is too low; an estimate that is less than the true or actual value
▸ verb: make too low an estimate of ("He underestimated the work that went into the renovation")
▸ verb: make a deliberately low estimate
▸ verb: assign too low a value to ("Don't underestimate the value of this heirlooom-you may sell it at a good price")
▸ Also see underestimate