Ignotum per ignotius (Latin for "the unknown by the more unknown") describes an explanation that is less familiar than the concept it would explain.
An example would be: "The oven felt hot because of Fourier's law." It is unlikely that a person unfamiliar with the hotness of ovens would be enlightened by a reference to a fundamental law of physics.
That said, since these explanations could enlighten people in theory, ignotum per ignotius is not strictly a fallacy, but a criticism of an argument on rhetorical grounds, stating that such an argument is not useful in a particular context.