'atelectatic' originates ultimately from Greek via New Latin; it derives from Greek 'atelēs' meaning 'incomplete' + 'ektasis' meaning 'extension, expansion', passed into New Latin as 'atelectasis', and then formed into English with the suffix '-ic' to yield 'atelectatic'.

'atelectatic' changed from the New Latin/medical noun 'atelectasis' (from Greek elements) and the adjective form was created by adding the English/Neo-Latin suffix '-ic', eventually becoming the modern English adjective 'atelectatic'.

Initially it meant 'relating to incomplete expansion (of the lung)', and this medical meaning has largely been retained in modern usage as 'relating to or affected by atelectasis'.