sea coconut
/ˈˌsiː ˈˌkəʊkənʌt/noun
1The coco de mer, Lodoicea maldivica; the fruit or seed of this.
2The fruit of the bussu palm, Manicaria saccifera, which has a hard and very rough outer shell containing two or three seeds, and may be dispersed by water. Also called sea apple. rare.
Origin
Early 18th century. From sea + coconut.