I want to say something of this sort:
The word "res" differs from the word "rex" by one letter.
In "Lexicon totius Latinitatis" I saw under the term "dama":
"[Dama] differt a capreis solis cornibus, quæ in anteriorem pártem habet incurvata"
My understating is that this formulation from the above quote indeed answers my question. Namely:
X differt a Y(albative) Z(ablative)
([Dama] differs from caprea only by the antlers)
But I'm not sure that my understating is correct. I have hard time trying to validate this by other examples. Also I wonder of other alternatives to formulate such an expression.