Able to be declined in grammar; (of a word) capable of changing its form to show different cases, numbers, or genders.
From decline + -able. In grammar, this describes words that follow the rules of declension, unlike indeclinable words which stay the same.
In Latin, every noun is declinable, but prepositions are NOT—they're indeclinable—which is why scholars call prepositions 'invariable words' because they refuse to change their form no matter what.
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