"incomplete expansion of the lungs," 1836, medical Latin, from Greek ateles "imperfect, incomplete," literally "without an end," (from a-, privative prefix, + telos "completion") + ektosis "extention." Related: Atelectatic.
atelectasis at·e·lec·ta·sis (āt'l-ěk'tə-sĭs)
The absence of gas from all or a part of the lungs, due to failure of expansion or resorption of gas from the alveoli.
A congenital condition characterized by the incomplete expansion of the lungs at birth.