Topping

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late Old English topp (noun), of Germanic origin; related to Dutch top ‘summit, crest’.

wiktionary

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From Middle English toppyng; equivalent to top +‎ -ing.

etymonline

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topping (n.)

"an act of putting a top on," c. 1500, verbal noun from top (v.). Meaning "an act of cutting the top off" is from 1510s. Meaning "top layer of a food" is from 1839,