Merriam-Webster's Collegiate® Dictionary, 11th Edition
WHENCE
I. adverb
Etymology: Middle English whennes, from whenne whence (from Old English hwanon) + -s, adverb suffix, from -s, genitivesingular ending; akin to Old High German hwanān whence, Old English hwā who
Date: 13th century
from what place, source, or cause ,
II. conjunction
Date: 13th century
from what place, source, or cause ,
2. from or out of which place, source, or cause , by reason of which fact ; wherefore