'heterochromasia' originates from Greek, specifically the elements 'hetero-' and 'chroma', where 'hetero-' meant 'different' and 'chroma' meant 'color', combined with the noun-forming suffix '-asia'.

'heterochromasia' entered medical Neo-Latin/late 19th-century medical usage as 'heterochromasia' and was adopted into English medical literature to denote differences in color or staining.

Initially it meant 'difference in color' in a general sense, but over time it evolved into specialized medical senses: 'variation in staining intensity of cells or tissues' and the sense 'difference in iris color' (often treated as synonymous with heterochromia).