Source : Webster's Revised Unabridged Dictionary (1913)

Underrate \Un`der*rate"\, v. t.
   To rate too low; to rate below the value; to undervalue.
   --Burke.

Underrate \Un"der*rate`\, n.
   A price less than the value; as, to sell a thing at an
   underrate. --Cowley.

Source : WordNet®

underrate
     v : 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" [syn: {underestimate}]
         [ant: {overestimate}]