'oedematous' originates from New Latin via Greek, specifically the word 'oedema' from Greek 'oidēma', where the root 'oidē-' meant 'to swell'.

'oedematous' changed from the New Latin/Medieval Latin formation related to 'oedema' (from Greek 'oidēma') into English usage as the adjective 'oedematous'.

Initially it meant 'relating to a swelling' and over time it has retained this medical meaning of 'having or caused by an accumulation of fluid (swelling)'.