天火字典

英日字典：おうとうき

おうとうき

奥陶紀：

(n)

(obsc)

(See オルドビス紀)
Ordovician period
桜桃忌：

(n)

(太宰治)
anniversary that celebrates author Dazai Osamu's birthday, and incidentally, the day his body was found after he was involved in a double suicide