pertinacity

From Middle French pertinacité, from Old French pertinace (“obstinate, stubborn”).

pertinacity (usually uncountable, plural pertinacities)

1. The state or characteristic of being pertinacious.
   • 1846, E.A.Poe, The Black Cat

     With my aversion to this cat, however, its partiality for myself seemed to increase. It followed my footsteps with a pertinacity which it would be difficult to make the reader comprehend.

   • 1851, Nathaniel Hawthorne, The House of Seven Gables, ch. 19:

     Again and again, however, and half a dozen other agains, with the inexorable pertinacity of a child intent upon some object important to itself, did he renew his efforts for admittance.

• pertinaciousness, resolve, stubbornness, tenacity

• antipyretic