expression, ichidan verb
Archaic expression meaning to calm one's anger or excitement. Not used in modern Japanese; replaced by 腹が立たなくなる or 気が静まる.
「腹がいる」は古い言い方で、今は「腹の虫が治まる」などと言う。
"Hara ga iru" is an old expression; nowadays one says things like "hara no mushi ga osamaru."