estimateestimateestimatesestimatedestimating2verb (estimates, estimating, estimated)to say how much you think something will cost, how big something is, or how long it will take to do something: The builders estimated that it would take a week to repair the roof.estimateestimateestimates1nouna guess about the size or cost of something before you have all the facts and figures: Can you give me a rough estimate of how many people will be there?