Einstein cross · noun1
From Einstein (“Albert Einstein”) + cross. From the shape of a cross, of four points at roughly square angles around a central object, caused by distortions in the path of light's travel due to Einsteinian relativity (Albert Einstein's general relativity) creating four points out of a single light source behind the off-center central object. (An on-center central object results in an Einstein ring.).
Einstein Cross · proper noun2
A capitalization of Einstein cross.
Etymology from Wiktionary, CC BY-SA 4.0.