In a manner relating to or characteristic of a decagon; along the lines or patterns of a ten-sided shape.
From decagonal + -ly (adverb suffix). The suffix -ly converts the adjective decagonal into an adverb that describes how something happens or is arranged.
Decagonally is a rare word that shows the incredible flexibility of English—by stacking suffixes (decagon + -al + -ly), we can describe not just shapes but the way things are arranged or oriented!
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