'aphtha' originates from Greek, specifically the word 'aphthē' (ἄφθα), where the root meant 'a sore or ulcer'.

'aphtha' passed into Late Latin as 'aphtha' (used in medical Latin), then into Middle English and modern English largely unchanged as 'aphtha'.

Initially it referred generally to sores or ulcerative eruptions, and over time the meaning narrowed in common medical usage to denote small mucous-membrane ulcers (especially in the mouth).