Examples from the Web for understructure
By the June of that year the understructure of the Pier was finished, and the rest was advancing with the speed of paper-hanging.Mushroom Town|Oliver Onions
Stan saw a Liberator smack into a bursting shell that exploded against her understructure.
The hair at the back of his neck lifted as his understructure raked across the hatch cover of the Jerry.
And I confess that at this close view of the understructure of a polygamous career, I was weak enough to feel scandalized.Captain Macedoine's Daughter|William McFee