noun
BAD : I decided to take a big stick with me, just as a prevention.
GOOD : I decided to take a big stick with me, just as a precaution.
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prevention = the act of stopping something from happening: 'The police are also concerned with the prevention of crime.'
precaution = an action taken in an attempt to avoid possible danger, damage, injury, etc: 'Some drivers have had alarms fitted as an extra precaution.