'blennorrhagic' originates from New Latin/medical formation, ultimately from Greek elements: 'blenno-' from Greek 'blennos' meaning 'mucus' and '-rrhagic' from Greek 'rhēgnynai'/'rhein' (via the suffix '-rrhagia') meaning 'to flow' or 'a bursting forth'.

'blennorrhagic' developed from the noun 'blennorrhagia' (used in Neo-Latin/medical Latin), which itself comes from Greek 'blennorrhagia' ('blenno-' + '-rrhagia'); the adjective form entered English medical usage in the 19th century as 'blennorrhagic'.

Initially the root referred to a 'mucous discharge' ('blennorrhagia'); over time the adjective form came to mean 'relating to or producing such a mucous discharge' ('blennorrhagic').