British spelling of favorableness; the quality of being favorable; the degree to which circumstances or treatment are advantageous.
From British spelling of favorable (favour + -able) plus -ness. The difference between American and British English spellings with 'favor/favour' dates to 18th-century standardization.
Americans dropped the 'u' from favor/favour to save ink and time, which is exactly the kind of lazy efficiency that makes English spelling so confusing!
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