In a way that heats or produces heat; with heating effect or intensity.
From 'heating' (present participle of 'heat') plus the adverbial suffix '-ly' (from Old English '-lice'). This formation creates an adverb describing the manner or quality of the action 'heating.'
Adverbs ending in '-ingly' are often quite rare and poetic—they're not as common as '-ingly' words from adjectives, yet they beautifully capture the nature of an action itself rather than just its manner.
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