Dashing

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Middle English (in the sense ‘strike forcibly against’): probably symbolic of forceful movement and related to Swedish and Danish daska .

wiktionary

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From Middle English daschande, equivalent to dash +‎ -ing.

From Middle English dasshyng, dasshynge, equivalent to dash +‎ -ing.

etymonline

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dashing (adj.)

1796, "performed with dash, impetuous;" from 1801 as "given to cutting a dash," a colloquial expression attested from 1786 (see cut (v.)) for "acting brilliantly," from dash (n.) in the sense of "showy appearance" (1715). Earlier in the sense of "splashing" (1620s), which replaced dashende (mid-15c.) as a present-participle adjective. Related: Dashingly.