assign too low a value to; "Don't underestimate the value of this heirlooom-you may sell it at a good price"
make a deliberately low estimate; "The construction company wanted the contract badly and lowballed"
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"
An estimate that is too low.