[n] an estimation that is too low; an estimate that is less than the true or actual value
[v] make too low an estimate of; "he underestimated the cost of the renovation"; "Don't underestimate the danger of such a raft trip on this river"
[v] make a deliberately low estimate; "The construction compnay wanted the contract badly and lowballed"
[v] assign too low a value to; "Don't underestimate the value of this heirlooom-you may sell it at a good price"