declinable

From decline +‎ -able.

• (UK) IPA^(key): /dɪˈklaɪnəbəɫ/

declinable (not comparable)

1. (grammar) Capable of being declined.
   • 1985, Robert Burchfield, The English Language, Oxford: Oxford University Press, page 152:

     It is obvious that the system in present-day English is radically different, and that the notion of case (i.e. a form or modification of a declinable word) is now of very little significance.

• indeclinable

• “declinable”, in OneLook Dictionary Search.