In a way that promotes or maintains good physical and mental condition; with attention to wellness.
From 'healthy' (Old English 'hælth', meaning wholeness or soundness) plus the adverbial suffix '-ly', which converts adjectives to adverbs indicating manner or degree.
The '-ily' ending in 'healthily' is actually a merger of two suffixes: '-y' (making an adjective) plus '-ly' (making an adverb), which is why it looks a bit awkward compared to just '-ly' alone—English speakers stack suffixes like building blocks!
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