Heavily

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Old English hefig, of Germanic origin; related to Dutch hevig, also to heave.

wiktionary

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From Middle English hevely, hevyliche, from Old English hefiġlīċe(“heavily; grievously”), equivalent to heavy +‎ -ly.

etymonline

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heavily (adv.)

Old English hefiglice "violently, intensely; sorrowfully; sluggishly," from hefig (see heavy (adj.)) + -ly (2). Meaning "with much weight" is from early 14c.