'pus-filled' originates from Modern English as a compound of the noun 'pus' and the past participle 'filled'. 'pus' comes from Latin 'pus' meaning 'pus', and 'filled' derives from Old English 'fyllan' (via Middle English 'fillen'), where the root meant 'to make full.'

'pus' entered English from Latin 'pus' (used in medical/Latin contexts) and remained as the medical term in Middle and Modern English. 'Fill' evolved from Old English 'fyllan' → Middle English 'fillen' → Modern English 'fill'; the past participle 'filled' combined with 'pus' in Modern English to form the descriptive compound 'pus-filled.'

Initially the elements literally meant 'full of pus' (i.e., 'made full with pus'); over time the compound has retained this literal medical meaning and is used descriptively for wounds, abscesses, or lesions that contain pus.