The variable name used to be a field of Poly, but it was changed in V2.0.0 by jverzani · Pull Request #310 · JuliaMath/Polynomials.jl · GitHub, which says:
breaking changes, the main one is using the type system to hold the indeterminate rather than use a field to hold the indeterminate. The advantage is this plays better with Julia’s promotion mechanisms so matrices of polynomials requires much less fuss.
The question is, why do you care about the polynomial symbol in your application? Why not just call it x and be done with it? It seems like this mostly matters for multivariate polynomials?