Archaic or rare form relating to duplicity; characterized by deceitfulness or double-dealing.
From 'duplicity' (from Latin 'duplicitas', meaning twofoldness or deception) with the suffix '-ous' (full of). This is an extremely rare variant, as 'duplicitous' is the standard modern form.
English loves its word variants, but 'duplicious' mostly died out—replaced by 'duplicitous.' It's like watching evolution in real time as languages choose which words survive!
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