Impetus /noun / im·pe·tus
The word impetus is a noun that refers to a driving force that inspires someone to take action. The “driving force” can refer to encouragement, stimulation, or internal or external motivation.
In a Sentence
She had a strong impetus to start her own business after seeing the success of her friends' ventures.
Having this sense of impetus helped make all the hard work worthwhile, and she now enjoys running her own business with plenty of ambition and drive.
"Impetus" comes from the Latin words impendere, meaning "to stretch out or to hurl," and tus, meaning "a push, a throwing."