Lexicography

In American English usage, the name can be capitalized or spelled in lowercase interchangeably, either when used completely or prefixed with "the" Many consciously spell the name of the planet with a capital, both as "Earth" or "the Earth". This is to distinguish it as a good noun, distinct from the senses of the term as a count noun or verb. Oxford Spelling recognizes the lowercase form as the most common, with the capitalized form as an alternative of it. Another convention that is very ordinary is to spell the name with a capital when occurring absolutely and lowercase when preceded by "the". The term almost completely exists in lowercase when appearing in common phrases, even without "the" preceding it.

Terms that refer to the Earth can use the Latin origin terr-, as in terraform and terrestrial. Another Latin root is tellur-, which is used in language such as tellurian and tellurium. Such terms derive from Latin terra and tellus, which refer variously to the world, the element earth, the earth goddess and so forth. Scientific terms such as geography, geocentric and geothermal use the Greek prefix geo, from (again meaning "earth"). In many skill fiction books and video games, Earth is referred to as Terra or Gaia. Astronauts refer to the Earth as "Terra Firma".