Definition of "indeclinable" [in•de•clin•a•ble]

• Without grammatical inflection. (adjective)
• Of or being a word that lacks grammatical inflection though belonging to a form class whose members are usually inflected. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "A statement was put forward on Vicipaedia for gas, indeclinable, as the Latin term, because the located scientific usages of the term in Latin texts (from 1652, which even gives the etymology) are just that."
• "By 1794, writers of scientific Latin, perhaps fed up with the non-Latin sound of gas as an indeclinable, had changed to gas, - is, a noun of the third declension."
• "In politics, reform is an indeclinable and urgent task to bring about changes in legislation so that our young democracy can move forward, strengthen the direction taken by political parties and fine-tune our institutions, restoring values and providing more transparency in all types of public activity."