1) of place: from where, from what condition
2) of origin or source: from what author or giver
3) of cause: how is that?, how can that be?
Part of Speech: adverb
From the base of G4213 with enclitic adverb of origin; from which (as interrogitive) or what (as relative) place, state, source or cause: - whence.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root πόθεν; click on the second column to search for that grammatical form of the root πόθεν; click on the third column to search for that word and grammatical form; click on the total to search for the root πόθεν.