Reckoner
Pronunciation : Reck"on*er
Part of Speech : n.
Definition : Defn: One who reckons or computes; also, a book of calculation, tables, etc., to assist in reckoning. Reckoners without their host must reckon twice. Camden.
Source : Webster's Unabridged Dictionary, 1913
Merriam-Webster's Everyday Language Reference Set: Includes: The Merriam-Webster Dictionary, The Merriam-Webster Thesaurus, and The Merriam-Webster Vocabulary Builder