From gentle +‎ -ship.

gentleship (uncountable)

1. (obsolete) The deportment or conduct of a gentleman.
   • a. 1569 (date written), Roger Ascham, edited by Margaret Ascham, The Scholemaster: Or Plaine and Perfite Way of Teaching Children, to Vnderstand, Write, and Speake, the Latin Tong,[…], London: […] John Daye,[…], published 1570, →OCLC:

     men will […]have more gentleship in their hat than in their head

• “gentleship”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.