computer vs subtracter

computer and subtracter both are nouns.

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

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

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

computer (noun)	subtracter (noun)
a machine for performing calculations automatically	a machine that subtracts numbers
an expert at calculation (or at operating calculating machines)	a person who subtracts numbers