While a definite answer to this would require intense linguistical research, and might not ever yield a certain answer, we could think about this in terms of cultural information that has survived the longest: religion and mythology. read more
Earth had many names before "earth" , like"terra" cognates with sanskrit "dhara" , in sanskrit bhu is also a famous word for earth. But most interesting is Egyptian Geb .There Geb is masculine word. Then its "zam, gau and geo" in persian, sanskrit and greek . which are words for the earth. read more
The name Earth originated from the 8th century Anglo-Saxon word erda which means ground or soil. read more