'pustule' originates from Latin, specifically the word 'pustula', where 'pustula' meant 'a blister or small pimple'.

'pustule' entered English via Late Latin/Old French (Latin 'pustula', Old French 'pustule') and eventually became the modern English word 'pustule'.

Initially, it meant 'a small blister or pimple', and over time its meaning has remained largely the same, referring to a pus-filled lesion.