The quality or state of being capable of being directed, steered, or controlled, especially regarding airships or aircraft.
From dirigible (capable of being directed) plus -ity (a suffix forming abstract nouns), creating a noun for the abstract concept of directability.
Early airships were called 'dirigibles' because—unlike hot air balloons—they could be steered; 'dirigibility' is basically the fancy noun version of 'steerability.'
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