Definitions

1. noun

A person who has crossed the equator, especially one who has done so while at sea.

“The shellback received a certificate for having crossed the equator during the voyage.”

2. noun

A sailor who has completed a certain number of days at sea, especially one who has done so on a whaling ship.

“The shellback was celebrated for his many years of experience at sea.”

3. adjective

Of or relating to a person who has crossed the equator, especially one who has done so while at sea.

“The shellback ceremony is a traditional ritual for sailors who have crossed the equator.”