underbelly

As nouns the difference between underbelly and abdomen

is that underbelly is (figuratively) the side which is not normally seen while abdomen is .

In figuratively|lang=en terms the difference between underpin and underbelly

is that underpin is (figuratively) to give support to; to corroborate while underbelly is (figuratively) the side which is not normally seen.

As a verb underpin

is to support from below with props or masonry.

As a noun underbelly is

(figuratively) the side which is not normally seen.