Sentence:  She had however another motive, beside her obedience, to accompany the old gentleman in the chase; for by her presence she hoped in some measure to restrain his <WSD>impetuosity</WSD>, and to prevent him from so frequently exposing his neck to the utmost hazard. 
Meaning of the word marked with <WSD> tags:  The quality of making rash or arbitrary decisions, especially in an impulsive or forceful manner.