I am talking about a relation that is what Wikipedia describes as [left-unique and right-unique][1]. I never heard these terms before, but I have heard of the alternatives (injective and functional). The question is, *which terminology do you recommend*? Should I include short definitions? (The context is a text in the area of formal methods. I'm not sure if this helps.)

These are some trade-offs that I see:

 - I think that *left-unique* and *right-unique* are not widely known, but I'm not sure at all.
 - *functional* is overloaded
 - *injective* sounds too fancy (subjective, of course)
 - *left-unique* and *right-unique* are symmetric (good, of course)

  [1]: http://en.wikipedia.org/wiki/Relation_(mathematics)#Special_types_of_binary_relations