/ ɪmˈpʌlʃn; NAmE / noun ( formal )
1.
[ C ] a strong desire to do sth
2.
[ U ] a reason for doing sth :
Lack of food and water provided much of the impulsion for their speed.
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WORD ORIGIN
late Middle English (in the sense the action or an instance of impelling ): via Old French from Latin impulsio(n-) , from the verb impellere , from in- towards + pellere to drive.