mid-15c., from Old French estimer "to estimate, determine" (14c.), from Latin aestimare "to value, determine the value of, appraise," perhaps ultimately from *ais-temos "one who cuts copper," i.e. mints money (but de Vaan finds this "not very credible"). At first used as we would now use estimate; sense of "value, respect" is 1530s. Related: Esteemed; esteeming.
Others are reading
Definitions of estimator
an expert at calculation (or at operating calculating machines);