estimator vs subtracter

estimator and subtracter both are nouns.

Word	Noun	Adjective	Verb	Adverb
estimator	Yes	No	No	No
subtracter	Yes	No	No	No

As nouns, subtracter is a hyponym of estimator; that is, subtracter is a word with a more specific, narrower meaning than estimator:

Other hyponyms of estimator include adder, number cruncher, actuary, statistician.

estimator (noun)	subtracter (noun)
an expert at calculation (or at operating calculating machines)	a machine that subtracts numbers
	a person who subtracts numbers