Eli and I made this list in college. We couldn’t come up with a good adjective for X.

Abelian
Bounded
Continuous
Discrete
Effective
Functorial
Generic
Hausdorff
Integrable
Japanese
K-theoretic
Linear
Monotonic
Normal
Orthogonal
Paracompact
Quintic
Rational
Self-adjoint
Transverse
Universal
Vacuous
Well-defined
Yoneda
Zonal