noun
concealed nail; hidden nail
A nail driven in so that its head is hidden, often used in fine woodworking for a clean finish.
この建具には隠し釘が使われている。
Concealed nails are used in this joinery.
Compound of 隠し (kakushi, 'hiding') + 釘 (kugi, 'nail'). The reading くぎ becomes voiced to ぐぎ due to rendaku.