an upward stroke, especially of a pen or pencil, or of a piston in a vertical cylinder.

1820–30; up- + stroke1 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
upstroke (ˈʌpˌstrəʊk)
1.  a.  an upward stroke or movement, as of a pen or brush
 b.  the mark produced by such a stroke
2.  the upward movement of a piston in a reciprocating engine

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Example sentences
Unlike other birds, hummingbirds get a portion of their lift during the
  upstroke of their wings.
Modern birds use a similar bone in flight, drawing their wings toward their
  bodies during an upstroke.
When a snowy owl flies, its wings make a powerful downstroke and a quick
If the penguin is stroking, you can expect some of them upstroke and the other
  ones downstroke.
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