'embryo' originates from Greek, specifically the word 'ἔμβρυον (embruon),' where 'en-' meant 'in' and 'bruō' meant 'to swell.'

'ἔμβρυον' transformed into the Latin word 'embryo,' and eventually became the modern English word 'embryo' through Middle English.

Initially, it meant 'to swell within,' but over time it evolved into its current meaning of 'early developmental stage of an organism.'