noun
Etymology: probably translation of New Latin quarta dimensio
1. : a dimension in addition to the three dimensions length, breadth, and thickness that is assumed to exist in order to satisfy certain mathematical analogies and that in the theory of relativity constitutes the time coordinate used along with the rectangular coordinates x, y, z to locate a point (as for recording an event)
2. : something outside the range of ordinary experience
a fourth dimension of meaning that transcends … the issue of clarity versus obscurity — Peter Viereck