indeclinable

 
Pronunciation: /ˌɪndɪˈklʌɪnəb(ə)l/

adjective

Grammar
  • (of a noun, pronoun, or adjective in a highly inflected language) having no inflections.

Origin:

late Middle English: via French from Latin indeclinabilis, from in- 'not' + declinabilis 'able to be inflected' (see decline)