Cardinal (adjective)

1. Of prime importance; fundamental.
2. Relating to the cardinal points of a compass.
3. Relating to the Roman Catholic Church and the office of cardinal.

Origin:

Late middle english: from old french cardinel, from latin cardinalis, from cardo, cardin- hinge.

Examples:

1. This is a cardinal rule that must be followed.
2. The cardinal points of the compass are north, south, east, and west.
3. The cardinal led the service at the church.
4. The cardinal virtues are prudence, justice, fortitude, and temperance.
5. The cardinal changes of the seasons are winter, spring, summer, and fall.