Lobachevskyian
The sense that's already there mentions his work on non-Euclidian geometry, right? It says, paraphrasing, relating to the person Lobachevsky or his work on non-Euclidian geometry.
But Lobachevskyan also can mean specifically "hyperbolic geometry". I think that sense should be in a separate definition, because its only tangentially related to "of or related to Nikolai Lobachevsky".
But the point is, that the first definition already says, "Of or pertaining ... to his work ... on non-Euclidian geometry".
Maybe it should be two definitions, but if so, you need to remove the part from the first one about the non-Euclidian geometry so that the definitions aren't redundant. So in that case, one would be only about the person and the other only about the geometry.