The principal duty of the full membership is to pick host cities.

The principal duty of the virtues is to work miracles on earth.

His principal duty for many years was keeping the peace in Offaly.

Their principal duty is making sure the two little princesses are safe and well.

On the day of the wedding, her principal duty is to provide practical and emotional support.

It is true that I told her her principal duty would be to hold my hand.

A man with a family ought to make it his principal duty to bring them up in the best way possible.

His principal duties were in the field of management.

His principal duties related to the provision of air-raid shelters.

His principal duty was to negotiate loans with the Fuggers, on commission.