noun
buttonhole
Refers to the slit or hole in fabric through which a button is passed.
このシャツのボタン穴が小さすぎて、ボタンが通らない。
The buttonholes on this shirt are too small; the buttons won't go through.
ボタン means 'button', while ボタン穴 specifically refers to the hole for the button.
Compound of ボタン (button, from Portuguese botão) and 穴 (hole).