Of or being a word that lacks grammatical inflection though belonging to a form class whose members are usually inflected.
Without grammatical inflection.
The definition of indeclinable is a grammar term that is a word that must be determined from its context because it does not have anything added to show a grammatical category such as tense, gender, mood or number.
An example of an indeclinable word is the word "must" or the word "coffee."
(grammar) A word that is not grammatically inflected.
Not declinable; having no case inflections.