Collapse of an expanded lung (especially in infants)

• Also failure of pulmonary alveoli to expand at birth

WordNet Word definitions in WordNet
n. collapse of an expanded lung (especially in infants); also failure of pulmonary alveoli to expand at birth

Wiktionary Word definitions in Wiktionary
n. (context medicine English) The collapse of a part of or the whole lung caused by inner factors rather than a pneumothorax.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
"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 .

Wikipedia Word definitions in Wikipedia
Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It may affect part or all of a lung. It is usually not bilateral. It is a condition where the alveoli are deflated down to little or no volume, as distinct from ...