whereby

• POS: Pronoun, Adverb
• HYPHEN: where=by

CIDE DICTIONARY

whereby, adv. 

•  By which; -- used relatively.  Shak.  [1913 Webster]
•  By what; how; -- used interrogatively.  [1913 Webster]

  "Whereby shall I know this?"  [1913 Webster]

OXFORD DICTIONARY

whereby, conj. by what or which means.

ROGET THESAURUS

whereby

Instrumentality

N instrumentality, aid, subservience, subserviency, mediation, intervention, medium, intermedium, vehicle, hand, agency, minister, handmaid, midwife, accoucheur, accoucheuse, obstetrician, gobetween, cat's-paw, stepping-stone, opener, key, master key, passkey, latchkey, open sesame, passport, passe-partout, safe-conduct, password, instrument, expedient, means, instrumental, useful, ministerial, subservient, mediatorial, intermediate, intervening, conducive, through, by, per, whereby, thereby, hereby, by the agency of, by dint of, by virtue of, in virtue of, through the medium of, along with, on the shoulders of, by means of, by the aid of, with the aid of, per fas et nefas, by fair means or foul, somehow, somehow or other, by hook or by crook.