In a manner relating to or having the form of a hexagon; arranged or oriented in a hexagonal pattern.
From 'hexagonal' plus the adverbial suffix '-ly' (in the manner of). This adverb allows description of actions or arrangements that follow hexagonal patterns.
When describing how snowflakes form, crystallographers use this term because ice crystals always arrange themselves hexagonally due to the molecular geometry of water—which is why every snowflake has six-fold symmetry.
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