Most etymologies of silhouette note that Etienne de Silhouette served as the French financial minister in 1759, during the Seven Years’ War. He famously pinched pennies — or whatever the most useless French coin was back then — in order to support the military effort. During this time, the act of cutting black paper in a person’s likeness became a cost-effective alternative to, you know, having them painted or having marble chipped until it looked like them, and the association between Silhouette’s thriftiness and this style of craft has stuck ever since.
For a moment, however, just focus on what a silhouette is, as far as a black form you might hand on the wall. Given how we think about black and white, it’s a negative space drawing — instead of the black representing a body, the white around it could represent everything outside that body. Now hold onto that, because it’s important. Etymonline gives all the standard background for silhouette but also goes a step further, into what the last name meant before it was attached to penny-pinching, shadows and those portraits you buy at Disneyland. The name comes from Basque. In fact, in its pre-Frenchified state, it may have been Zuloeta, with the -eta meaning “an abundance of” and zulo meaning “cave” or “hole.” If you focus on caves and holes essentially being voids — absences of the materials that surround them — then it’s weirdly appropriate that silhouette has come to mean what it does, because that’s exactly how a silhouette can be read: a lot of empty space.