The quality of being capable of being extended or stretched; the degree to which something can be made longer or wider.
From 'extendible' plus the suffix '-ity', which turns adjectives into abstract nouns describing their quality. Ultimately from Latin extendere.
Software engineers love this word—when they talk about 'extendibility,' they mean how easily you can add new features or make a program bigger without breaking what already works, which is a fundamental design challenge!
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