'megaspore' originates from Greek elements 'mega-' and 'spora' (via New Latin), where 'mega-' meant 'large' and 'spora' meant 'seed' or 'that which is sown'.

'megaspore' was formed in scientific English by combining the Greek prefix 'mega-' with 'spore' (from New Latin 'spora') in 19th-century botanical usage to name the larger of two spore types.

Initially it simply meant 'large spore'; over time it became the technical term for the larger spore in heterosporous plants that gives rise to the female gametophyte.