Adam Clarke on Job 20:20

Surely he shall not feel quietness in his belly - I have already remarked that the word בטן beten, which we translate belly, often means in the sacred Scriptures the whole of the human trunk; the regions of the thorax and abdomen, with their contents; the heart, lungs, liver, etc., and consequently all the thoughts, purposes, and inclinations of the mind, of which those viscera were supposed to be the functionaries. The meaning seems to be, "He shall never be satisfied; he shall have an endless desire after secular good, and shall never be able to obtain what he covets."