hiatus

a break or interruption in the continuity of a work, series, action, etc.

a missing part; gap or lacuna:

any gap or opening.

Grammar, Prosody. the coming together, with or without break or slight pause, and without contraction, of two vowels in successive words or syllables, as in see easily.

Anatomy. a natural fissure, cleft, or foramen in a bone or other structure.