FOSS, or FOSSÆ, in Fortification, a ditch or moat. The word in French is formed from the participle fossus, of the Latin verb fodio, I dig.
Foss, Fossa, in Anatomy, a kind of cavity in a bone, with a large aperture, but no exit or perforation. When the aperture is very narrow it is called a sinus.
Foss is particularly used for the cavity or indentation in the back part of the neck.