cooked, well done
胹 centers on food that has been thoroughly heated: cooked or well done. The idea is that something has been prepared by heat until it is ready to eat.
胹 combines ⺼ (flesh/meat) with 而, which likely contributes the sound. The character expresses cooking meat until it is done.
The left side ⺼ is flesh or meat, and the right side 而 looks like a pot on a stove. Picture meat being cooked in a pot until it is well done.
For ジ, imagine a chef saying 'Gee, this meat is well done!' as he takes it out of the pot: Gee -> ジ.