Definition of "partly"

Five minutes into the game the Black Cats were facing a mountain, partly because of West Brom's newly-found ruthlessness in front of goal but also as a result of the home side's defensive generosity.

2011 October 1, Phil Dawkes, “Sunderland 2-2 West Brom”, in BBC Sport

Clara's cultural cache soon gave way to Betty Boop, the iconic cartoon flapper created partly in her image by animator Grim Natwick.

2012, Christoper Zara, Tortured Artists: From Picasso and Monroe to Warhol and Winehouse, the Twisted Secrets of the World's Most Creative Minds, part 1, chapter 1, 27

The dirty secret of the internet is that all this distraction and interruption is immensely profitable. Web companies like to boast about […] and so on. But the real way to build a successful online business is to be better than your rivals at undermining people's control of their own attention. Partly, this is a result of how online advertising has traditionally worked: advertisers pay for clicks, and a click is a click, however it's obtained.

2013 June 21, Oliver Burkeman, “The tao of tech”, in The Guardian Weekly, volume 189, number 2, page 48