Is this why is it called a "nut"????

Nut: from the German nut, (pronounced noot)
"nf. mortise, recess or groove in a piece of wood or another material that fits together with a corresponding projecting piece of material, joint, slot,

Hmm, so the noot is actually the recess at the starting end of the fingerboard where the nut sits into. Just that the actual "projecting piece of material" sitting inside the nut eventually came around to become the nut.

Or maybe it's the string "grooves" or noots in the bone piece sitting in the noot at the starting end of the fingerboard that gave the bone piece the name nut.