Whistling

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Old English (h)wistlian (verb), (h)wistle (noun), of Germanic origin; imitative and related to Swedish vissla ‘to whistle’.

wiktionary

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From Middle English whistlynge, equivalent to whistle +‎ -ing.

From Middle English whistlinge, whystlynge, equivalent to whistle +‎ -ing.

etymonline

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whistling (n.)

Old English hwistlung, verbal noun from hwistlian (see whistle (v.)).