Allow a "different from" relationship?

[azaroth42]

The opposite of equivalent, this would be when two entities are different rather than the same but might get confused.

For example the concept of "velvet" is most likely to be the textile (http://vocab.getty.edu/aat/300133711) but could be a bright white photographic paper, or "satin" could be the textile, but could be a sheen of paint, amongst many other sets of homonyms.

[kkdavis14]

This would be very useful for e.g. Yale units to tell LUX when they already know things are different from each other. A good example is taxon homonymy from Yale Peabody:
viola (the plant) & viola (the insect)
ambronia (the plant) & ambronia (the lizard)

They've already done the work internally and have the subject knowledge to distinguish these taxon, this seems like the best way to leverage it.