'catarrhal' originates from English formation based on the noun 'catarrh', ultimately from Greek via Latin; Greek 'katarrhē' (from 'kata-' + 'rhein') where 'kata-' meant 'down' and 'rhein' meant 'to flow'.

'catarrh' came into Late Latin/Medieval Latin as 'catarrhus' from Greek 'katarrhē', and English formed the adjective 'catarrhal' by attaching the suffix '-al' to 'catarrh', producing the modern English 'catarrhal'.

Initially the Greek root described a 'flowing down' (excess discharge), which developed into the medical sense 'excessive mucous discharge/inflammation' and the adjective now means 'relating to catarrh' or 'characterized by mucous inflammation'.