computer vs reckoner

computer and reckoner both are nouns.

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

As nouns, computer and reckoner are synonyms defined as:

computer and reckoner: an expert at calculation (or at operating calculating machines)

Other synonyms of computer include calculator, estimator, figurer.

computer (noun)	reckoner (noun)
a machine for performing calculations automatically	a handbook of tables used to facilitate computation
an expert at calculation (or at operating calculating machines)	an expert at calculation (or at operating calculating machines)