'fossa' (plural 'fossae') originates from Classical Latin, specifically the word 'fossa' meaning 'ditch' or 'trench'.

'fossa' in Latin (meaning 'ditch') was adopted into New Latin/Modern Latin usage in scientific contexts and then borrowed into English as 'fossa' (plural 'fossae'), retaining the sense of a dug-out or hollowed place and later specialized in anatomy and geology.

Initially it meant 'ditch' or 'trench' in Latin; over time it evolved into the modern English/medical sense of 'a shallow depression or hollow' used especially for anatomical depressions.