Implacable is an adjective that means unstoppable or relentless.

The origin of our word of the day is the Latin word placare (pla CAR ay) which means ‘to calm’ or ‘to soothe.’ The prefix I-M is used to indicate ‘not’ or in this case, ‘cannot be.’ Something that cannot be calmed or soothed is implacable.

For example: Our team’s implacable spirit may have been the reason we won the championship. We may not have had much talent, but we compensated with our relentless drive.