The Collaborative International Dictionary of English v.0.48:
midair \mid*air"\ n. some point in the air; above ground level; as, the planes collided in midair; also used attributively; as, a midair collision. [WordNet 1.5 +PJC]WordNet (r) 3.0 (2006):
midair n 1: some point in the air; above ground level; "the planes collided in midair"