impetus-n; 2 Senses

Sense Number 1: drift

Commentary: impulsion - a force that moves something along

Examples:
His desire for change was the impetus behind the revolution.

Mappings:
WordNet 2.0 Sense Numbers: 1

Sense Number 2: act of applying force

Commentary: IMPETUS[+event] the act of applying force suddenly

Examples:
The impetus knocked him over.

Mappings:
WordNet 2.0 Sense Numbers: 2