Definify.com
Webster 1913 Edition
Somewhen
Some′whenˊ
,adv.
 At some indefinite time. 
[R.] 
Definition 2025
somewhen
somewhen
English
Adverb
somewhen (not comparable)
-  at some time; indefinitely; some time or other, sometime
-  1864, Browning, Robert, “Mr. Sludge, "The Medium"”, in Wikisource, line 505, retrieved 2012-01-18:
- Out of the drift of facts, whereby you learn / What some was, somewhere, somewhen, somewhy?
 
 -  2002, Marc Lange, “What Is Spatiotemporal Locality?”, in An Introduction to the Philosophy of Physics: Locality, Fields, Energy, and Mass (Science / Philosphy), Wiley-Blackwell, ISBN 9780631225010, page 4:
- An event is a particular thing that happens somewhere and somewhen.
 
 -  2008, Michael F. Wagner, “Chapter One”, in The Enigmatic Reality of Time (Science / Physics), Brill, ISBN 9789004170254, page 26:
- … things always exist or occur somewhen as well. They exist or occur whenever — at whatever times-when — they in fact exist or occur, and not somewhen else.
 
 -  2009, Marta Randall, “Secret Rider”, in Robert Siverberg, editor, Trips in Time: Time Travel Tales (Collection of Short Stories) (SciFi), Wildside Press, ISBN 9781434404466, page 120:
- Somewhen, curling through the intricacies of tau, John/Johan still lived. Somewhen on this very planet he lived, …
 
 
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References
- Century Dictionary and Cyclopedia, somewhen