In a manner related to or promoting combustion; in a way that burns or causes burning.
From 'combustive' plus the adverbial suffix '-ly.' This creates a manner adverb describing how something relates to or causes combustion.
When engineers describe a fuel as behaving 'combustively efficiently,' they mean it's optimized for the burning process itself. It's a precision word that separates 'how burnable' from 'how well it burns in this specific situation.'
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