'Reckoner' definitions:

Definition of 'reckoner'

From: WordNet
noun
An expert at calculation (or at operating calculating machines) [syn: calculator, reckoner, figurer, estimator, computer]
noun
A handbook of tables used to facilitate computation [syn: reckoner, ready reckoner]

Definition of 'Reckoner'

From: GCIDE
  • Reckoner \Reck"on*er\ (r[e^]k"'n*[~e]r), n. One who reckons or computes; also, a book of calculations, tables, etc., to assist in reckoning. [1913 Webster]
  • Reckoners without their host must reckon twice. --Camden. [1913 Webster]