noun
bed warmer; foot warmer
A traditional Japanese heating device placed under bedding or used to warm the feet. Modern versions are often electric.
寒い夜はあんかを布団に入れて寝ます。
On cold nights, I put a bed warmer in the futon and sleep.
祖母は昔ながらの炭のあんかを使っている。
My grandmother uses an old-fashioned charcoal bed warmer.
The kanji 行火 literally means 'traveling fire', suggesting a portable heat source. The reading あんか is of uncertain origin, possibly from a Chinese-derived reading or a native Japanese term.