homa stick; prayer stick
A wooden stick used in Shingon and other Buddhist goma fire rituals. Prayers or wishes are written on it and it is ritually burned before a deity to seek blessings.
I wrote my wish on a homa stick and had it burned at the goma altar.
From 護摩 (goma, 'homa fire ritual', from Sanskrit homa) + 木 (ki, 'wood'), with rendaku voicing of 木 to ぎ.