'planet-like' originates from Modern English as a compound of 'planet' + the suffix '-like' (meaning 'similar to'). 'Planet' ultimately comes from Greek 'planētēs' via Latin and Old French; '-like' comes from Old English suffix formed from 'līc' meaning 'body/form'.

'planet' comes from Greek 'planētēs' (meaning 'wanderer'), passed into Latin as 'planeta' and into Middle English as 'planet'; the suffix '-like' developed from Old English 'līc' into a productive Middle English suffix '-like', forming adjectives that mean 'having the form or nature of'. Combined in Modern English as the compound 'planet-like'.

Initially the elements referred to a 'wanderer' (planet) and 'form/similarity' (‑like); combined, the compound has come to mean 'resembling a planet' in appearance or characteristics.