'hemihydrate' originates from Greek elements via Modern scientific coinage, specifically the prefix 'hemi-' (from Greek 'hemi') meaning 'half' and 'hydrate' (from Greek 'hydōr' / root 'hydr-') meaning 'water'.

'hemihydrate' was formed in Modern scientific nomenclature by combining the Greek-derived prefix 'hemi-' and the element 'hydrate'; it entered English as a technical chemical term in the 19th–20th century and has been used in mineralogy and inorganic chemistry.

Initially it meant literally 'half-water' (a word-for-word composition), but over time it acquired the precise chemical meaning 'a compound containing half a mole of water per formula unit (e.g., CaSO4·0.5H2O)'.