ETYM Latin, a bent surface, a curve, the folds or bosom of a garment, etc., a bay. Related to Sine.
Any of various air-filled cavities especially in the bones of the skull.
Cavity, especially of skull bone.
Sinus frontalis, Nebenräume der Nase von wechselnder Größe u. Gestalt im Stirnbein über den inneren Augenwinkeln.