'pyrogenous' originates from New Latin, specifically the word 'pyrogenus', where 'pyr-' (from Greek 'pyr') meant 'fire' and '-genus'/'-gen' meant 'born' or 'producing'.

'pyrogenous' changed from Neo-Latin 'pyrogenus' (built from Greek roots) and was adopted into scientific English usage to describe substances or processes that produce heat or cause fever, eventually becoming the modern English adjective 'pyrogenous'.

Initially it meant 'producing or generating fire/heat' in a literal or figurative sense, and over time it has been used especially in scientific and medical contexts to mean 'producing heat or causing fever'; this core meaning has largely remained consistent.