gaea

As a letter s

is the letter s with a.

As a proper noun gaea is

(greek mythology) a greek goddess: the personification of the earth, and one of the primordial deities from whom all the others descend.

As proper nouns the difference between gaea and rhea

is that gaea is a Greek goddess: the personification of the earth, and one of the primordial deities from whom all the others descend while Rhea is a Titan, the daughter of Uranus and Gaia, the mother of Demeter, Hades, Hera, Hestia, Poseidon, and Zeus.

As a noun rhea is

a large flightless bird of the genus Rhea, native to South America.