Fossil word is a term used in linguistics to describe a word that is no longer in everyday use but is still preserved in certain expressions or phrases.

The fossil waters found in the underground reservoirs are millions of years old.

The Fosbury flops at the track meet were impressive.

My two foster fathers have been a great support to me.

Fositesland is an obsolete name for Heligoland.

My friend's last name is Foshee.

The Foshees are coming to the party tonight.

The Foskeys are a close-knit family.

My friend's last name is Foskey.

The Fosdicks are a well-known family in the town.