primarily

The idea of fitting a crane to an engine for shunting duties, primarily in works yards, appears to have originated with the North London Railway engine in 1872.

1951 October, H. C. Casserley, “Crane Engines”, in Railway Magazine, page 660

These spectacles aren't calls for a Hobbesian war of all against all by some insurgent movement that, however dangerous, would have First Amendment protection. They're driven primarily by institutions that we as sovereign citizens created to serve our purposes.

2013 January 25, Jim Sleeper, Daniel J. H. Greenwood, “To Stop Gun Violence, We Need to Remember We Can Regulate Corporate Speech and Advertising”, in The Atlantic, archived from the original on 08 Jul 2014

But now a study has shown that most cancers are primarily caused by bad luck rather than poor lifestyle choices or defective DNA.

2015 January 1, Sarah Knapton, “Most cancers are caused by bad luck not genes or lifestyle, say scientists”, in The Telegraph, archived from the original on 30 Aug 2015

Zika virus disease is caused by a virus transmitted primarily by Aedes mosquitoes, which bite during the day.

2018 July 20, “Zika virus”, in World Health Organization, archived from the original on 17 Apr 2019