An Etymological Dictionary of the German Language/Annotated/verteidigen
verteidigen, verb, ‘to defend, maintain, justify,’ from the equivalent Middle High German verteidingen, vertagedingen (usually tagedingen), weak verb, of which the most frequent meaning is ‘to plead before a tribunal, settle and adjust by agreement.’ Allied to Middle High German tagedinc, teidinc (g), ‘a lawsuit fixed for a certain date, court-day, negotiation, assembly’ (with the meaning ‘gossip, talk,’ compare Teiding). Old High German tagading, ‘legal summons, negotiations,’ is based on tag in the sense of ‘fixed period,’ and ding, ‘judicial proceedings,’ Compare Dutch verdedigen.