'anhydraemic' originates from New Latin and Greek, specifically from Greek 'an-' meaning 'without' + 'hydōr' meaning 'water' + 'haima' meaning 'blood', via the noun 'anhydraemia' plus the adjectival suffix '-ic.'

'anhydraemia' was formed in 19th-century medical Latin/English from Greek roots; the adjective 'anhydraemic' developed in English from this noun. The US spelling simplified the digraph to 'anhydremic' (ae → e).

Initially, it meant 'without normal water in the blood' in a strict medical sense; it is still technical but may be used more broadly to indicate severe dehydration in clinical contexts.