'earthlikeness' originates from English, specifically formed by combining 'earth' + 'like' + the nominalizing suffix '-ness', where 'earth' referred to the planet or ground, 'like' meant 'similar to', and '-ness' created a noun denoting a state or quality.

'earth' comes from Old English 'eorþe' meaning 'ground, soil, the world'; 'like' comes from Old English 'lic'/'lician' meaning 'body, form' or 'to be like'; the suffix '-ness' derives from Old English '-nes(s)e' used to form nouns. These elements combined in Modern English to form the compound 'earthlike' and then the noun 'earthlikeness'.

The component words originally referred separately to 'ground/planet' and 'similarity'; over time the compound came to denote the specific idea of resemblance to Earth—in modern use often specialized to describe planetary habitability or Earth-like characteristics.