Definitions of 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
    Example: "He underestimated the work that went into the renovation"
  • verb:   make a deliberately low estimate
  • verb:   assign too low a value to
    Example: "Don't underestimate the value of this heirlooom-you may sell it at a good price"