also: いかのこう
cuttlebone
The internal shell of a cuttlefish, often used as a calcium supplement for pet birds or for polishing.
I bought a cuttlebone for my parakeet.
Kanji spelling for イカ; less common and may be considered old-fashioned or literary.
Compound of イカ (squid/cuttlefish) and 甲 (shell/armor). The exact historical derivation is straightforward.