I am talking about a relation that is what Wikipedia describes as left-unique and right-unique. 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)