The plural form referring to multiple instances or types of the quality of becoming tired or worn out.
From 'fatiguability' (capacity to be tired) + '-ies' plural suffix. A technical term primarily used in materials science and engineering to discuss different wear properties.
When engineers test different metals, they compare their 'fatiguabilities'—essentially rating which metals get tired and break down the fastest. It's a grammatical quirk that the plural form exists mostly in technical papers rather than everyday speech.
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