assiduousness

assiduous +‎ -ness

assiduousness (uncountable)

1. The state or property of being assiduous; industriousness.
   • 1856, William L. G. Smith, The Life and Times of Lewis Cass‎, page 323:

     Finding that his health was failing, because of the assiduousness which a proper discharge of the duties of the position demanded the year round, he acquainted the President with his desire to withdraw from public duties.

   • 2016 October 3, Tad Friend, “Sam Altman’s Manifest Destiny”, in The New Yorker‎:

     I found his assiduousness alarming at first, then gradually endearing. When I remarked, after a few long days together, that he never seemed to visit the men’s room, he said, “I will practice going to the bathroom more often so you humans don’t realize that I’m the A.I.”