An Etymological Dictionary of the German Language/Annotated/-zig

by Friedrich Kluge

-zig, suffix for forming the tens, from Middle High German -zic (g), Old High German -zug; compare zwanzig. In dreißig, from Middle High German drî-ȥec, Old High German drî-ȥug, there appears a different permutation of the t of Gothic tigus, ‘ten’; compare Anglo-Saxon -tig, English -ty. Gothic tigu- (from pre-Teutonic dekú-) is a variant of taíhan, ‘ten.’ See zehn.