word-forming element meaning "over, above, beyond, in addition," especially in words from Anglo-French and Old French, from Old French sour-, sor-, sur-, from Latin super "above, over," from PIE root *uper "over."
early 14c., "obligatory contribution levied by a sovereign or government," from Anglo-French tax, Old French taxe, and directly from Medieval Latin taxa, from Latin taxare (see tax (v.)). Related: Taxes. Tax-deduction is from 1942; tax-shelter is attested from 1961.
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<a href="https://www.etymonline.com/word/surtax">Etymology of surtax by etymonline</a>
Harper, D. (n.d.). Etymology of surtax. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/surtax