The quality or state of being able to be added; the property that allows something to be combined with something else.
From 'addible' (able to be added) plus suffix '-ity,' which creates nouns from adjectives. Traces back to Latin addere (to add) plus Germanic '-able.'
Addibility seems like a strange word until you realize mathematicians needed a term for why numbers can combine but some abstract things can't—it's actually a philosophy-of-math concept hiding in plain English.
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