reckoner vs adder

reckoner and adder both are nouns.

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

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

Other hyponyms of reckoner include number cruncher, actuary, statistician, subtracter.

reckoner (noun)	adder (noun)
a handbook of tables used to facilitate computation	small terrestrial viper common in northern Eurasia
an expert at calculation (or at operating calculating machines)	a machine that adds numbers
	a person who adds numbers