'oosphere' originates from New Latin and ultimately from Greek: Greek 'ōon' (ᾠόν) meaning 'egg' + Greek 'sphaira' meaning 'sphere' or 'ball'.

'oosphere' formed in New Latin/modern scientific usage from the Greek elements 'ōon' and 'sphaira'; it entered English via scientific Latin/Neo-Latin usage in botany and biology.

Initially a compound meaning 'egg-sphere' (referring to the egg's rounded form), it came to be used specifically for the female reproductive cell of certain lower plants and algae.