1) An appraisal that is too high 2) Appraisal 3) Assign too high a value to 4) Estimate 5) Estimation 6) Make too high an estimate of 7) Overappraisal 8) Overestimation 9) Overvaluation 10) Take too seriously 11) To judge too highly 1) Fudge 2) Miscalculate 3) Misjudge 4) Overappraisal 5) Overestimation 6) Overrate 7) Overrating 8) Overreckoning 9) Overvaluation 10) Overvalue 
• (v. t.) To estimate too highly; to overvalue. • (n.) An estimate that is too high; as, an overestimate of the vote.
[Verb] To think that something is bigger or better than it really is.
O`ver·es'ti·mate transitive verb To estimate too highly; to overvalue. 
[n] - an appraisal that is too high 2. [n] - a calculation that results in an estimate that is too high 3. [v] - make too high an estimate of
An estimate that is greater than the exact answer 
overestimation noun a calculation that results in an estimate that is too high