from The American Heritage® Dictionary of the English Language, 4th Edition
- conj. In accordance with which; by or through which.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. By what, in which direction; how
- adv. By which.
- adv. Where.
from the GNU version of the Collaborative International Dictionary of English
- adv. By which; -- used relatively.
- adv. By what; how; -- used interrogatively.
from The Century Dictionary and Cyclopedia
- By what? how? why?
- By which, in any sense of the word by.
From where + by. (Wiktionary)