This is a curved fissure on the lateral wall of the middle meatus. It sits between the uncinate process inferiorly and the ethmoidal bulla superiorly. It connects the middle meatus to the anterior ethmoidal air cells and in some skulls the frontonasal duct to the frontal sinus.

Semilunar comes from the Latin semi meaning half and luna meaning moon. Hiatus is a Latin term meaning a cleft or gap. It takes its origin from the Latin verb hiare meaning to yawn or gape.

Hiatus semi-lunaire