fourth dimension 
noun
1A postulated spatial dimension additional to those determining length, area, and volume.Their momentum along the fourth dimension would appear as additional mass in three dimensions, so we would observe heavy photons or heavy electrons, for example....
- The conflicting claims of class and confession represent an additional, necessary fourth dimension to this paradigm.
- Granted, to the hypercube, the fourth dimension is only another spatial dimension, but to us, the fourth dimension seems to be temporal.
2Time regarded as analogous to linear dimensions.As things change over time, a fourth dimension needs to be added to politics - and my way of doing this is to argue that what is the right course of action changes with time....
- Is time just a fourth dimension which, together with the three dimensions of space, helps to comprise a unitary four-dimensional manifold in which all physical objects and events somehow reside?
- Time as the fourth dimension is basically just a mathematical gimmick to make some relativity equations easier to work with.