There is another word for belly. It is not honorific. It is the word hara.
Hara is a plain form of the honorific o-naka 中
hara 腹 はら- the belly, the stomach
Here are some uses of hara -
hara ga itamu 腹が痛む - to have stomach pains 腹 はら
hara o tateru 腹を立てる- to get or become upset; angry
hara ga tatsu - when speaking of one's self - That upsets me, or that really ticks me off or that really "p***es me off" etc.
An easy way to remember the other Japanese word for stomach, o-naka, would be to think
You onaka'd up!" (お-中ed up) You are knocked up!
Towards Better Japanese Ganbatte ne! Do Your Best! Makurasuki