noun
obi pillow; obi pad
A small oval pad worn under the obi knot to add volume and shape, especially for formal kimono styles.
振袖を着るときは、帯枕を使って帯をふっくらと見せる。
When wearing a furisode, you use an obi pillow to make the obi look fuller.
Compound of 帯 (obi, 'sash') and 枕 (makura, 'pillow'), referring to its function as a cushion-like support for the obi knot.