From precipitant + -ance.

precipitance (uncountable)

1. Precipitancy. [from 17th c.]
   • 1748, [Samuel Richardson], “Letter XX”, in Clarissa. Or, The History of a Young Lady: […], volume (please specify |volume=I to VII), London: […] S[amuel] Richardson;  […], →OCLC ↗:

     I gasped, at this frightful precipitance—I was going to open with warmth against it.

   • c. 1794, Jane Austen, Lady Susan:

     We have been hurried on by our feelings to a degree of Precipitance which ill accords with the claims of our Friends, or the opinion of the World.