A continuation of the series.
ignotum per ignotius: Latin [ɪgˈnəʊtʊm pər ɪgˈnəʊtɪʊs]
(Philosophy) an explanation that is obscurer than the thing to be explained
[literally: the unknown by means of the more unknown]
If you ask some of my syntax students, they would say that this applies to quite a few of the official definitions found in syntactic theory (sister precedence, c-command, the principle of modification) and I can't say that I blame them initially.
Defintion from thefreedictionary.com