In fields like geometry and numerical methods for solving differential equations we often use words like sub-face and sub-edge, referring to parts of a geometrical object. For instance, a cube has 6 faces and 12 edges. It is often necessary to refer to parts of these objects as sub-edges and sub-faces.. In the academic literature, all three forms ("sub edge", "sub-edge", and "subedge") are in use.. What would be the correct/preferred form to use?
(The word "sub-edge" cannot be found in the Oxford Dictionary, whereas "subface", can be found meaning "The undersurface of a rock formation", which is not the meaning of subface I was looking for..)