By necessity; necessarily; as a result of unavoidable circumstances (archaic form).
From Old French 'by' + 'nécessité' (necessity). This archaic English adverb combines the preposition 'by' with a form related to 'destination' or 'necessity' to convey that something happens out of necessity rather than choice.
This word is so archaic that even libraries don't see it often anymore—it's like finding a medieval compass that nobody's used in 300 years, but it beautifully shows how English compressed 'by necessity' into one word.
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