spike; dog nail
A large, heavy nail used in timber framing and traditional carpentry; the head often resembles a dog's head or the nail is driven deep like a dog's tooth.
The carpenter used dog nails to secure the beam.
Thick dog nails are driven into the pillars of this old house.
Compound of 犬 (inu, 'dog') and 釘 (kugi, 'nail'). The name likely comes from the nail's large size or the shape of its head, which may resemble a dog's head.