'blood-clotting' originates from Modern English compounding of 'blood' and the present participle 'clotting' (from 'clot' + '-ing').

'clot' comes from Old English 'clott' meaning 'lump'; it passed into Middle English as 'clot' and later formed the present participle 'clotting', which combined with 'blood' to yield the compound 'blood clotting' and the hyphenated form 'blood-clotting'.

Initially, 'clot' primarily meant 'a lump' (physical lump); over time the combined phrase came to denote the physiological process of blood forming a lump (coagulation) and the adjective describing things related to that process.