Whence is defined as from what time or place.(adverb)
An example of whence is asking a person where they are from by saying "From whence do you come?"
Whence means from or to where.(conjunction)
An example of whence is saying you'll send a person back to where they came from; from when they came.
See whence in Webster's New World College Dictionary
Origin: ME whennes (< whenne, when + adv. gen. -s), replacing OE hwanan
See whence in American Heritage Dictionary 4
Origin: Middle English whennes
Origin: : whenne, whence (from Old English hwanon; see kwo- in Indo-European roots)
Origin: + -es, genitive sing. suff.; see -s3. Usage Note: The construction from whence has been criticized as redundant since the 18th century. It is true that whence incorporates the sense of from: a remote village, whence little news reached the wider world. But from whence has been used steadily by reputable writers since the 14th century, most notably in the King James Bible: “I will lift up mine eyes unto the hills, from whence cometh my help” (Psalms). Such a respectable precedent makes it difficult to label the construction as incorrect. Still, it may be observed that whence (like thence) is most often used nowadays to impart an archaic or highly formal tone to a passage, and that this effect is probably better realized if the archaic syntax of the word—without from—is preserved as well.
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