›[I or T]to think that something is or will be greater or more important than it really is: grossly/wildly overestimateI think we have grossly overestimated the pace of growth.Most people overestimate what they can achieve in a day and underestimate what they can achieve in a year.Assess your potential earnings honestly - don't overestimate.
›[T]to think that someone is better at doing something, more intelligent, etc. than they really are: I thought they would pick it up very quickly, but I overestimated them.
overestimationnoun[C or U]›Part of the problem was gross overestimation of ticket sales.