indeclinable: Meaning and Definition of

in•de•clin•a•ble

Pronunciation: (in"di-klī'nu-bul), [key]
— adj. Gram.
  1. not capable of being declined; having no inflected forms: used esp. of a word belonging to a form class most of whose members are declined, as the Latin adjective decem, “ten.”
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.