at·e·lec·ta·sis 
(ăt′l-ĕktə-sĭs)
(ăt′l-ĕktə-sĭs)n. pl. at·e·lec·ta·ses (-sēz′)
1. The absence of gas from all or part of the lung, due to failure of expansion of the alveoli.
2. A congenital condition characterized by incomplete expansion of the lungs.
[New Latin : Greek atelēs, incomplete (a-, not; see A-1 + telos, end; see TELO-) + Greek ektasis, stretching out (from ekteinein, to stretch out : ek-, out; see ECTO- + teinein, to stretch; see EPITASIS).]