The quality or state of being fatal; the characteristic of causing death or resulting in destruction or ruin.
From 'fatal' (from Latin 'fatalis' meaning relating to fate/death) combined with the noun suffix '-ness'. This creates an abstract noun describing the essence of being fatal.
The fascinating thing about 'fatal' is that it conflates two different concepts—something that causes death AND something related to fate (from the same Latin root). So 'fatalness' carries this echo of the idea that death is written in the stars, not just biologically inevitable.
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