'hetero-' originates from Greek, specifically the word 'heteros', where 'heter-' meant 'other, different'.

'heteros' passed into New Latin/Modern scientific coinage as the combining form 'hetero-' and was adopted into English (mainly in scientific and scholarly compounds) in the 19th century, producing words such as 'heterogeneous' and 'heterosexual'.

Initially it meant 'other, different' in Ancient Greek; over time this core meaning has been retained, though specific senses (e.g. 'opposite sex' in 'heterosexual') developed in modern usage.