In a manner that has or maintains equal sides; in the way that an equilateral figure is constructed.
From 'equilateral' with the adverbial suffix '-ly'. It allows 'equilateral' to function as a modifier describing how something is done or arranged.
This adverb is rare because we usually just say 'equilaterally' to mean 'with equal sides,' but you might encounter it in mathematical proofs or technical descriptions of symmetric arrangements.
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