Pronunciation: (lu-kyOO'nu),[key] —n., —pl.-naePronunciation: (-nē),[key]-nas. 1. a gap or missing part, as in a manuscript, series, or logical argument; hiatus.
2. Anat.one of the numerous minute cavities in the substance of bone, supposed to contain nucleate cells.
3. Bot.an air space in the cellular tissue of plants.