An estimator is not the guess itself. It is the person — or, in a numbers class, the method — that tries to judge the value, size, speed, or cost of something without counting every last piece. In ordinary work, that is often a job. A building estimator looks at a plan and says, roughly, how much money and time the job will take. Insurance uses estimators too. The number they give you is the estimate: “The estimator said about two hundred thousand dollars.” In statistics, an estimator is not a person. It is a rule or formula that uses a small set of data to guess a true number you cannot see all of. The everyday core is the same: this is the one who, or that which, does the estimating. Though actually, a lot of everyday English never says estimator at all. People say “the person who gave us the quote.” The job title and the statistics term are where the word is really alive. It is a dry, technical word — not praise, and not an insult.